// ---------------------------------------------------------------------------
// Copyright (c) 2019, Gregory Popovitch - greg7mdp@gmail.com
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Includes work from abseil-cpp (https://github.com/abseil/abseil-cpp)
// with modifications.
//
// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ---------------------------------------------------------------------------

#include <numeric>
#include "btree_test.h"

#ifdef _MSC_VER
    #pragma warning(disable: 4244 4100 4389)
#endif

namespace phmap {
    namespace test_internal {
        size_t BaseCountedInstance::num_instances_ = 0;
        size_t BaseCountedInstance::num_live_instances_ = 0;
        size_t BaseCountedInstance::num_moves_ = 0;
        size_t BaseCountedInstance::num_copies_ = 0;
        size_t BaseCountedInstance::num_swaps_ = 0;
        size_t BaseCountedInstance::num_comparisons_ = 0;

    }  // namespace test_internal
}  // namespace phmap


static const size_t test_values = 10000;

namespace phmap {
namespace priv {
namespace {

    using ::phmap::test_internal::CopyableMovableInstance;
    using ::phmap::test_internal::InstanceTracker;
    using ::phmap::test_internal::MovableOnlyInstance;
    using ::testing::ElementsAre;
    using ::testing::ElementsAreArray;
    using ::testing::IsEmpty;
    using ::testing::Pair;

#define PHMAP_INTERNAL_CHECK(condition, message)    \
    if (!(condition)) assert(0)

    template <typename T, typename U>
    void CheckPairEquals(const T &x, const U &y) {
        PHMAP_INTERNAL_CHECK(x == y, "Values are unequal.");
    }

    template <typename T, typename U, typename V, typename W>
    void CheckPairEquals(const std::pair<T, U> &x, const std::pair<V, W> &y) {
        CheckPairEquals(x.first, y.first);
        CheckPairEquals(x.second, y.second);
    }
}  // namespace

// The base class for a sorted associative container checker. TreeType is the
// container type to check and CheckerType is the container type to check
// against. TreeType is expected to be btree_{set,map,multiset,multimap} and
// CheckerType is expected to be {set,map,multiset,multimap}.
template <typename TreeType, typename CheckerType>
class base_checker {
public:
    using key_type = typename TreeType::key_type;
    using value_type = typename TreeType::value_type;
    using key_compare = typename TreeType::key_compare;
    using pointer = typename TreeType::pointer;
    using const_pointer = typename TreeType::const_pointer;
    using reference = typename TreeType::reference;
    using const_reference = typename TreeType::const_reference;
    using size_type = typename TreeType::size_type;
    using difference_type = typename TreeType::difference_type;
    using iterator = typename TreeType::iterator;
    using const_iterator = typename TreeType::const_iterator;
    using reverse_iterator = typename TreeType::reverse_iterator;
    using const_reverse_iterator = typename TreeType::const_reverse_iterator;

public:
    base_checker() : const_tree_(tree_) {}
    base_checker(const base_checker &x)
        : tree_(x.tree_), const_tree_(tree_), checker_(x.checker_) {}
    template <typename InputIterator>
    base_checker(InputIterator b, InputIterator e)
        : tree_(b, e), const_tree_(tree_), checker_(b, e) {}

    iterator begin() { return tree_.begin(); }
    const_iterator begin() const { return tree_.begin(); }
    iterator end() { return tree_.end(); }
    const_iterator end() const { return tree_.end(); }
    reverse_iterator rbegin() { return tree_.rbegin(); }
    const_reverse_iterator rbegin() const { return tree_.rbegin(); }
    reverse_iterator rend() { return tree_.rend(); }
    const_reverse_iterator rend() const { return tree_.rend(); }

    template <typename IterType, typename CheckerIterType>
    IterType iter_check(IterType tree_iter, CheckerIterType checker_iter) const {
        if (tree_iter == tree_.end()) {
            PHMAP_INTERNAL_CHECK(checker_iter == checker_.end(),
                                 "Checker iterator not at end.");
        } else {
            CheckPairEquals(*tree_iter, *checker_iter);
        }
        return tree_iter;
    }
    template <typename IterType, typename CheckerIterType>
    IterType riter_check(IterType tree_iter, CheckerIterType checker_iter) const {
        if (tree_iter == tree_.rend()) {
            PHMAP_INTERNAL_CHECK(checker_iter == checker_.rend(),
                                 "Checker iterator not at rend.");
        } else {
            CheckPairEquals(*tree_iter, *checker_iter);
        }
        return tree_iter;
    }
    void value_check(const value_type &x) {
        typename KeyOfValue<typename TreeType::key_type,
                            typename TreeType::value_type>::type key_of_value;
        const key_type &key = key_of_value(x);
        CheckPairEquals(*find(key), x);
        lower_bound(key);
        upper_bound(key);
        equal_range(key);
        contains(key);
        count(key);
    }
    void erase_check(const key_type &key) {
        EXPECT_FALSE(tree_.contains(key));
        EXPECT_EQ(tree_.find(key), const_tree_.end());
        EXPECT_FALSE(const_tree_.contains(key));
        EXPECT_EQ(const_tree_.find(key), tree_.end());
        EXPECT_EQ(tree_.equal_range(key).first,
                  const_tree_.equal_range(key).second);
    }

    iterator lower_bound(const key_type &key) {
        return iter_check(tree_.lower_bound(key), checker_.lower_bound(key));
    }
    const_iterator lower_bound(const key_type &key) const {
        return iter_check(tree_.lower_bound(key), checker_.lower_bound(key));
    }
    iterator upper_bound(const key_type &key) {
        return iter_check(tree_.upper_bound(key), checker_.upper_bound(key));
    }
    const_iterator upper_bound(const key_type &key) const {
        return iter_check(tree_.upper_bound(key), checker_.upper_bound(key));
    }
    std::pair<iterator, iterator> equal_range(const key_type &key) {
        std::pair<typename CheckerType::iterator, typename CheckerType::iterator>
            checker_res = checker_.equal_range(key);
        std::pair<iterator, iterator> tree_res = tree_.equal_range(key);
        iter_check(tree_res.first, checker_res.first);
        iter_check(tree_res.second, checker_res.second);
        return tree_res;
    }
    std::pair<const_iterator, const_iterator> equal_range(
        const key_type &key) const {
        std::pair<typename CheckerType::const_iterator,
                  typename CheckerType::const_iterator>
            checker_res = checker_.equal_range(key);
        std::pair<const_iterator, const_iterator> tree_res = tree_.equal_range(key);
        iter_check(tree_res.first, checker_res.first);
        iter_check(tree_res.second, checker_res.second);
        return tree_res;
    }
    iterator find(const key_type &key) {
        return iter_check(tree_.find(key), checker_.find(key));
    }
    const_iterator find(const key_type &key) const {
        return iter_check(tree_.find(key), checker_.find(key));
    }
    bool contains(const key_type &key) const {
        return find(key) != end();
    }
    size_type count(const key_type &key) const {
        size_type res = checker_.count(key);
        EXPECT_EQ(res, tree_.count(key));
        return res;
    }

    base_checker &operator=(const base_checker &x) {
        tree_ = x.tree_;
        checker_ = x.checker_;
        return *this;
    }

    int erase(const key_type &key) {
        size_t size = tree_.size();
        int res = (int)checker_.erase(key);
        EXPECT_EQ(res, tree_.count(key));
        EXPECT_EQ(res, tree_.erase(key));
        EXPECT_EQ(tree_.count(key), 0);
        EXPECT_EQ(tree_.size(), size - res);
        erase_check(key);
        return res;
    }
    iterator erase(iterator iter) {
        key_type key = iter.key();
        size_t size = tree_.size();
        size_t count = tree_.count(key);
        auto checker_iter = checker_.lower_bound(key);
        for (iterator tmp(tree_.lower_bound(key)); tmp != iter; ++tmp) {
            ++checker_iter;
        }
        auto checker_next = checker_iter;
        ++checker_next;
        checker_.erase(checker_iter);
        iter = tree_.erase(iter);
        EXPECT_EQ(tree_.size(), (size_t)checker_.size());
        EXPECT_EQ(tree_.size(), size - 1);
        EXPECT_EQ(tree_.count(key), count - 1);
        if (count == 1) {
            erase_check(key);
        }
        return iter_check(iter, checker_next);
    }

    void erase(iterator begin, iterator end) {
        size_t size = tree_.size();
        int count = std::distance(begin, end);
        auto checker_begin = checker_.lower_bound(begin.key());
        for (iterator tmp(tree_.lower_bound(begin.key())); tmp != begin; ++tmp) {
            ++checker_begin;
        }
        auto checker_end =
            end == tree_.end() ? checker_.end() : checker_.lower_bound(end.key());
        if (end != tree_.end()) {
            for (iterator tmp(tree_.lower_bound(end.key())); tmp != end; ++tmp) {
                ++checker_end;
            }
        }
        checker_.erase(checker_begin, checker_end);
        tree_.erase(begin, end);
        EXPECT_EQ(tree_.size(), checker_.size());
        EXPECT_EQ(tree_.size(), size - count);
    }

    void clear() {
        tree_.clear();
        checker_.clear();
    }
    void swap(base_checker &x) {
        tree_.swap(x.tree_);
        checker_.swap(x.checker_);
    }

    void verify() const {
        tree_.verify();
        EXPECT_EQ(tree_.size(), checker_.size());

        // Move through the forward iterators using increment.
        auto checker_iter = checker_.begin();
        const_iterator tree_iter(tree_.begin());
        for (; tree_iter != tree_.end(); ++tree_iter, ++checker_iter) {
            CheckPairEquals(*tree_iter, *checker_iter);
        }

        // Move through the forward iterators using decrement.
        for (int n = (int)tree_.size() - 1; n >= 0; --n) {
            iter_check(tree_iter, checker_iter);
            --tree_iter;
            --checker_iter;
        }
        EXPECT_EQ(tree_iter, tree_.begin());
        EXPECT_EQ(checker_iter, checker_.begin());

        // Move through the reverse iterators using increment.
        auto checker_riter = checker_.rbegin();
        const_reverse_iterator tree_riter(tree_.rbegin());
        for (; tree_riter != tree_.rend(); ++tree_riter, ++checker_riter) {
            CheckPairEquals(*tree_riter, *checker_riter);
        }

        // Move through the reverse iterators using decrement.
        for (int n = (int)tree_.size() - 1; n >= 0; --n) {
            riter_check(tree_riter, checker_riter);
            --tree_riter;
            --checker_riter;
        }
        EXPECT_EQ(tree_riter, tree_.rbegin());
        EXPECT_EQ(checker_riter, checker_.rbegin());
    }

    const TreeType &tree() const { return tree_; }

    size_type size() const {
        EXPECT_EQ(tree_.size(), checker_.size());
        return tree_.size();
    }
    size_type max_size() const { return tree_.max_size(); }
    bool empty() const {
        EXPECT_EQ(tree_.empty(), checker_.empty());
        return tree_.empty();
    }

protected:
    TreeType tree_;
    const TreeType &const_tree_;
    CheckerType checker_;
};

namespace {
    // A checker for unique sorted associative containers. TreeType is expected to
    // be btree_{set,map} and CheckerType is expected to be {set,map}.
    template <typename TreeType, typename CheckerType>
    class unique_checker : public base_checker<TreeType, CheckerType> {
        using super_type = base_checker<TreeType, CheckerType>;

    public:
        using iterator = typename super_type::iterator;
        using value_type = typename super_type::value_type;

    public:
        unique_checker() : super_type() {}
        unique_checker(const unique_checker &x) : super_type(x) {}
        template <class InputIterator>
        unique_checker(InputIterator b, InputIterator e) : super_type(b, e) {}
        unique_checker& operator=(const unique_checker&) = default;

        // Insertion routines.
        std::pair<iterator, bool> insert(const value_type &x) {
            size_t size = this->tree_.size();
            std::pair<typename CheckerType::iterator, bool> checker_res =
                this->checker_.insert(x);
            std::pair<iterator, bool> tree_res = this->tree_.insert(x);
            CheckPairEquals(*tree_res.first, *checker_res.first);
            EXPECT_EQ(tree_res.second, checker_res.second);
            EXPECT_EQ(this->tree_.size(), this->checker_.size());
            EXPECT_EQ(this->tree_.size(), size + tree_res.second);
            return tree_res;
        }
        iterator insert(iterator position, const value_type &x) {
            size_t size = this->tree_.size();
            std::pair<typename CheckerType::iterator, bool> checker_res =
                this->checker_.insert(x);
            iterator tree_res = this->tree_.insert(position, x);
            CheckPairEquals(*tree_res, *checker_res.first);
            EXPECT_EQ(this->tree_.size(), this->checker_.size());
            EXPECT_EQ(this->tree_.size(), size + checker_res.second);
            return tree_res;
        }
        template <typename InputIterator>
        void insert(InputIterator b, InputIterator e) {
            for (; b != e; ++b) {
                insert(*b);
            }
        }
    };

    // A checker for multiple sorted associative containers. TreeType is expected
    // to be btree_{multiset,multimap} and CheckerType is expected to be
    // {multiset,multimap}.
    template <typename TreeType, typename CheckerType>
    class multi_checker : public base_checker<TreeType, CheckerType> {
        using super_type = base_checker<TreeType, CheckerType>;

    public:
        using iterator = typename super_type::iterator;
        using value_type = typename super_type::value_type;

    public:
        multi_checker() : super_type() {}
        multi_checker(const multi_checker &x) : super_type(x) {}
        template <class InputIterator>
        multi_checker(InputIterator b, InputIterator e) : super_type(b, e) {}
        multi_checker& operator=(const multi_checker&) = default;

        // Insertion routines.
        iterator insert(const value_type &x) {
            size_t size = this->tree_.size();
            auto checker_res = this->checker_.insert(x);
            iterator tree_res = this->tree_.insert(x);
            CheckPairEquals(*tree_res, *checker_res);
            EXPECT_EQ(this->tree_.size(), this->checker_.size());
            EXPECT_EQ(this->tree_.size(), size + 1);
            return tree_res;
        }
        iterator insert(iterator position, const value_type &x) {
            size_t size = this->tree_.size();
            auto checker_res = this->checker_.insert(x);
            iterator tree_res = this->tree_.insert(position, x);
            CheckPairEquals(*tree_res, *checker_res);
            EXPECT_EQ(this->tree_.size(), this->checker_.size());
            EXPECT_EQ(this->tree_.size(), size + 1);
            return tree_res;
        }
        template <typename InputIterator>
        void insert(InputIterator b, InputIterator e) {
            for (; b != e; ++b) {
                insert(*b);
            }
        }
    };

    template <typename T, typename V>
    void DoTest(const char *, T *b, const std::vector<V> &values) {
        typename KeyOfValue<typename T::key_type, V>::type key_of_value;

        T &mutable_b = *b;
        const T &const_b = *b;

        // Test insert.
        for (size_t i = 0; i < values.size(); ++i) {
            mutable_b.insert(values[i]);
            mutable_b.value_check(values[i]);
        }
        ASSERT_EQ(mutable_b.size(), values.size());

        const_b.verify();

        // Test copy constructor.
        T b_copy(const_b);
        EXPECT_EQ(b_copy.size(), const_b.size());
        for (size_t i = 0; i < values.size(); ++i) {
            CheckPairEquals(*b_copy.find(key_of_value(values[i])), values[i]);
        }

        // Test range constructor.
        T b_range(const_b.begin(), const_b.end());
        EXPECT_EQ(b_range.size(), const_b.size());
        for (size_t i = 0; i < values.size(); ++i) {
            CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
        }

        // Test range insertion for values that already exist.
        b_range.insert(b_copy.begin(), b_copy.end());
        b_range.verify();

        // Test range insertion for new values.
        b_range.clear();
        b_range.insert(b_copy.begin(), b_copy.end());
        EXPECT_EQ(b_range.size(), b_copy.size());
        for (size_t i = 0; i < values.size(); ++i) {
            CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
        }

        // Test assignment to self. Nothing should change.
        b_range.operator=(b_range);
        EXPECT_EQ(b_range.size(), b_copy.size());

        // Test assignment of new values.
        b_range.clear();
        b_range = b_copy;
        EXPECT_EQ(b_range.size(), b_copy.size());

        // Test swap.
        b_range.clear();
        b_range.swap(b_copy);
        EXPECT_EQ(b_copy.size(), 0);
        EXPECT_EQ(b_range.size(), const_b.size());
        for (size_t i = 0; i < values.size(); ++i) {
            CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
        }
        b_range.swap(b_copy);

        // Test non-member function swap.
        swap(b_range, b_copy);
        EXPECT_EQ(b_copy.size(), 0);
        EXPECT_EQ(b_range.size(), const_b.size());
        for (size_t i = 0; i < values.size(); ++i) {
            CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
        }
        swap(b_range, b_copy);

        // Test erase via values.
        for (size_t i = 0; i < values.size(); ++i) {
            mutable_b.erase(key_of_value(values[i]));
            // Erasing a non-existent key should have no effect.
            ASSERT_EQ(mutable_b.erase(key_of_value(values[i])), 0);
        }

        const_b.verify();
        EXPECT_EQ(const_b.size(), 0);

        // Test erase via iterators.
        mutable_b = b_copy;
        for (size_t i = 0; i < values.size(); ++i) {
            mutable_b.erase(mutable_b.find(key_of_value(values[i])));
        }

        const_b.verify();
        EXPECT_EQ(const_b.size(), 0);

        // Test insert with hint.
        for (size_t i = 0; i < values.size(); i++) {
            mutable_b.insert(mutable_b.upper_bound(key_of_value(values[i])), values[i]);
        }

        const_b.verify();

        // Test range erase.
        mutable_b.erase(mutable_b.begin(), mutable_b.end());
        EXPECT_EQ(mutable_b.size(), 0);
        const_b.verify();

        // First half.
        mutable_b = b_copy;
        typename T::iterator mutable_iter_end = mutable_b.begin();
        for (size_t i = 0; i < values.size() / 2; ++i) ++mutable_iter_end;
        mutable_b.erase(mutable_b.begin(), mutable_iter_end);
        EXPECT_EQ(mutable_b.size(), values.size() - values.size() / 2);
        const_b.verify();

        // Second half.
        mutable_b = b_copy;
        typename T::iterator mutable_iter_begin = mutable_b.begin();
        for (size_t i = 0; i < values.size() / 2; ++i) ++mutable_iter_begin;
        mutable_b.erase(mutable_iter_begin, mutable_b.end());
        EXPECT_EQ(mutable_b.size(), values.size() / 2);
        const_b.verify();

        // Second quarter.
        mutable_b = b_copy;
        mutable_iter_begin = mutable_b.begin();
        for (size_t i = 0; i < values.size() / 4; ++i) ++mutable_iter_begin;
        mutable_iter_end = mutable_iter_begin;
        for (size_t i = 0; i < values.size() / 4; ++i) ++mutable_iter_end;
        mutable_b.erase(mutable_iter_begin, mutable_iter_end);
        EXPECT_EQ(mutable_b.size(), values.size() - values.size() / 4);
        const_b.verify();

        mutable_b.clear();
    }

    template <typename T>
    void ConstTest() {
        using value_type = typename T::value_type;
        typename KeyOfValue<typename T::key_type, value_type>::type key_of_value;

        T mutable_b;
        const T &const_b = mutable_b;

        // Insert a single value into the container and test looking it up.
        value_type value = Generator<value_type>(2)(2);
        mutable_b.insert(value);
        EXPECT_TRUE(mutable_b.contains(key_of_value(value)));
        EXPECT_NE(mutable_b.find(key_of_value(value)), const_b.end());
        EXPECT_TRUE(const_b.contains(key_of_value(value)));
        EXPECT_NE(const_b.find(key_of_value(value)), mutable_b.end());
        EXPECT_EQ(*const_b.lower_bound(key_of_value(value)), value);
        EXPECT_EQ(const_b.upper_bound(key_of_value(value)), const_b.end());
        EXPECT_EQ(*const_b.equal_range(key_of_value(value)).first, value);

        // We can only create a non-const iterator from a non-const container.
        typename T::iterator mutable_iter(mutable_b.begin());
        EXPECT_EQ(mutable_iter, const_b.begin());
        EXPECT_NE(mutable_iter, const_b.end());
        EXPECT_EQ(const_b.begin(), mutable_iter);
        EXPECT_NE(const_b.end(), mutable_iter);
        typename T::reverse_iterator mutable_riter(mutable_b.rbegin());
        EXPECT_EQ(mutable_riter, const_b.rbegin());
        EXPECT_NE(mutable_riter, const_b.rend());
        EXPECT_EQ(const_b.rbegin(), mutable_riter);
        EXPECT_NE(const_b.rend(), mutable_riter);

        // We can create a const iterator from a non-const iterator.
        typename T::const_iterator const_iter(mutable_iter);
        EXPECT_EQ(const_iter, mutable_b.begin());
        EXPECT_NE(const_iter, mutable_b.end());
        EXPECT_EQ(mutable_b.begin(), const_iter);
        EXPECT_NE(mutable_b.end(), const_iter);
        typename T::const_reverse_iterator const_riter(mutable_riter);
        EXPECT_EQ(const_riter, mutable_b.rbegin());
        EXPECT_NE(const_riter, mutable_b.rend());
        EXPECT_EQ(mutable_b.rbegin(), const_riter);
        EXPECT_NE(mutable_b.rend(), const_riter);

        // Make sure various methods can be invoked on a const container.
        const_b.verify();
        ASSERT_TRUE(!const_b.empty());
        EXPECT_EQ(const_b.size(), 1);
        EXPECT_GT(const_b.max_size(), 0);
        EXPECT_TRUE(const_b.contains(key_of_value(value)));
        EXPECT_EQ(const_b.count(key_of_value(value)), 1);
    }

    template <typename T, typename C>
    void BtreeTest() {
        ConstTest<T>();

        using V = typename remove_pair_const<typename T::value_type>::type;
        const std::vector<V> random_values = GenerateValuesWithSeed<V>(
            test_values, 4 * test_values,
            GTEST_FLAG_GET(random_seed));

        unique_checker<T, C> container;

        // Test key insertion/deletion in sorted order.
        std::vector<V> sorted_values(random_values);
        std::sort(sorted_values.begin(), sorted_values.end());
        DoTest("sorted:    ", &container, sorted_values);

        // Test key insertion/deletion in reverse sorted order.
        std::reverse(sorted_values.begin(), sorted_values.end());
        DoTest("rsorted:   ", &container, sorted_values);

        // Test key insertion/deletion in random order.
        DoTest("random:    ", &container, random_values);
    }

    template <typename T, typename C>
    void BtreeMultiTest() {
        ConstTest<T>();

        using V = typename remove_pair_const<typename T::value_type>::type;
        const std::vector<V> random_values = GenerateValuesWithSeed<V>(
            test_values, 4 * test_values,
            GTEST_FLAG_GET(random_seed));

        multi_checker<T, C> container;

        // Test keys in sorted order.
        std::vector<V> sorted_values(random_values);
        std::sort(sorted_values.begin(), sorted_values.end());
        DoTest("sorted:    ", &container, sorted_values);

        // Test keys in reverse sorted order.
        std::reverse(sorted_values.begin(), sorted_values.end());
        DoTest("rsorted:   ", &container, sorted_values);

        // Test keys in random order.
        DoTest("random:    ", &container, random_values);

        // Test keys in random order w/ duplicates.
        std::vector<V> duplicate_values(random_values);
        duplicate_values.insert(duplicate_values.end(), random_values.begin(),
                                random_values.end());
        DoTest("duplicates:", &container, duplicate_values);

        // Test all identical keys.
        std::vector<V> identical_values(100);
        std::fill(identical_values.begin(), identical_values.end(),
                  Generator<V>(2)(2));
        DoTest("identical: ", &container, identical_values);
    }

    template <typename T>
    struct PropagatingCountingAlloc : public CountingAllocator<T> {
        using propagate_on_container_copy_assignment = std::true_type;
        using propagate_on_container_move_assignment = std::true_type;
        using propagate_on_container_swap = std::true_type;

        using Base = CountingAllocator<T>;
        using Base::Base;

        template <typename U>
        explicit PropagatingCountingAlloc(const PropagatingCountingAlloc<U> &other)
            : Base(other.bytes_used_) {}

        template <typename U>
        struct rebind {
            using other = PropagatingCountingAlloc<U>;
        };
    };

    template <typename T>
    void BtreeAllocatorTest() {
        using value_type = typename T::value_type;

        int64_t bytes1 = 0, bytes2 = 0;
        PropagatingCountingAlloc<T> allocator1(&bytes1);
        PropagatingCountingAlloc<T> allocator2(&bytes2);
        Generator<value_type> generator(1000);

        // Test that we allocate properly aligned memory. If we don't, then Layout
        // will assert fail.
        auto unused1 = allocator1.allocate(1);
        auto unused2 = allocator2.allocate(1);

        // Test copy assignment
        {
            T b1(typename T::key_compare(), allocator1);
            T b2(typename T::key_compare(), allocator2);

            int64_t original_bytes1 = bytes1;
            b1.insert(generator(0));
            EXPECT_GT(bytes1, original_bytes1);

            // This should propagate the allocator.
            b1 = b2;
            EXPECT_EQ(b1.size(), 0);
            EXPECT_EQ(b2.size(), 0);
            EXPECT_EQ(bytes1, original_bytes1);

            for (int i = 1; i < 1000; i++) {
                b1.insert(generator(i));
            }

            // We should have allocated out of allocator2.
            EXPECT_GT(bytes2, bytes1);
        }

        // Test move assignment
        {
            T b1(typename T::key_compare(), allocator1);
            T b2(typename T::key_compare(), allocator2);

            int64_t original_bytes1 = bytes1;
            b1.insert(generator(0));
            EXPECT_GT(bytes1, original_bytes1);

            // This should propagate the allocator.
            b1 = std::move(b2);
            EXPECT_EQ(b1.size(), 0);
            EXPECT_EQ(bytes1, original_bytes1);

            for (int i = 1; i < 1000; i++) {
                b1.insert(generator(i));
            }

            // We should have allocated out of allocator2.
            EXPECT_GT(bytes2, bytes1);
        }

        // Test swap
        {
            T b1(typename T::key_compare(), allocator1);
            T b2(typename T::key_compare(), allocator2);

            int64_t original_bytes1 = bytes1;
            b1.insert(generator(0));
            EXPECT_GT(bytes1, original_bytes1);

            // This should swap the allocators.
            swap(b1, b2);
            EXPECT_EQ(b1.size(), 0);
            EXPECT_EQ(b2.size(), 1);
            EXPECT_GT(bytes1, original_bytes1);

            for (int i = 1; i < 1000; i++) {
                b1.insert(generator(i));
            }

            // We should have allocated out of allocator2.
            EXPECT_GT(bytes2, bytes1);
        }

        allocator1.deallocate(unused1, 1);
        allocator2.deallocate(unused2, 1);
    }

    template <typename T>
    void BtreeMapTest() {
        using value_type = typename T::value_type;
        using mapped_type = typename T::mapped_type;

        mapped_type m = Generator<mapped_type>(0)(0);
        (void)m;

        T b;

        // Verify we can insert using operator[].
        for (int i = 0; i < 1000; i++) {
            value_type v = Generator<value_type>(1000)(i);
            b[v.first] = v.second;
        }
        EXPECT_EQ(b.size(), 1000);

        // Test whether we can use the "->" operator on iterators and
        // reverse_iterators. This stresses the btree_map_params::pair_pointer
        // mechanism.
        EXPECT_EQ(b.begin()->first, Generator<value_type>(1000)(0).first);
        EXPECT_EQ(b.begin()->second, Generator<value_type>(1000)(0).second);
        EXPECT_EQ(b.rbegin()->first, Generator<value_type>(1000)(999).first);
        EXPECT_EQ(b.rbegin()->second, Generator<value_type>(1000)(999).second);
    }

    template <typename T>
    void BtreeMultiMapTest() {
        using mapped_type = typename T::mapped_type;
        mapped_type m = Generator<mapped_type>(0)(0);
        (void)m;
    }

    template <typename K, int N = 256>
    void SetTest() {
        using BtreeSet = phmap::btree_set<K>;
        using CountingBtreeSet =
            phmap::btree_set<K, std::less<K>, PropagatingCountingAlloc<K>>;
        BtreeTest<BtreeSet, std::set<K>>();
        BtreeAllocatorTest<CountingBtreeSet>();
    }

    template <typename K, int N = 256>
    void MapTest() {
        using BtreeMap = phmap::btree_map<K, K>;
        using CountingBtreeMap =
            phmap::btree_map<K, K, std::less<K>,
                             PropagatingCountingAlloc<std::pair<const K, K>>>;
        BtreeTest<BtreeMap, std::map<K, K>>();
        BtreeAllocatorTest<CountingBtreeMap>();
        BtreeMapTest<BtreeMap>();
    }

    TEST(Btree, set_int32) { SetTest<int32_t>(); }
    TEST(Btree, set_int64) { SetTest<int64_t>(); }
    TEST(Btree, set_string) { SetTest<std::string>(); }
    TEST(Btree, set_pair) { SetTest<std::pair<int, int>>(); }
    TEST(Btree, map_int32) { MapTest<int32_t>(); }
    TEST(Btree, map_int64) { MapTest<int64_t>(); }
    TEST(Btree, map_string) { MapTest<std::string>(); }
    TEST(Btree, map_pair) { MapTest<std::pair<int, int>>(); }

    template <typename K, int N = 256>
    void MultiSetTest() {
        using BtreeMSet = phmap::btree_multiset<K>;
        using CountingBtreeMSet =
            phmap::btree_multiset<K, std::less<K>, PropagatingCountingAlloc<K>>;
        BtreeMultiTest<BtreeMSet, std::multiset<K>>();
        BtreeAllocatorTest<CountingBtreeMSet>();
    }

    template <typename K, int N = 256>
    void MultiMapTest() {
        using BtreeMMap = phmap::btree_multimap<K, K>;
        using CountingBtreeMMap =
            phmap::btree_multimap<K, K, std::less<K>,
                                  PropagatingCountingAlloc<std::pair<const K, K>>>;
        BtreeMultiTest<BtreeMMap, std::multimap<K, K>>();
        BtreeMultiMapTest<BtreeMMap>();
        BtreeAllocatorTest<CountingBtreeMMap>();
    }

    TEST(Btree, multiset_int32) { MultiSetTest<int32_t>(); }
    TEST(Btree, multiset_int64) { MultiSetTest<int64_t>(); }
    TEST(Btree, multiset_string) { MultiSetTest<std::string>(); }
    TEST(Btree, multiset_pair) { MultiSetTest<std::pair<int, int>>(); }
    TEST(Btree, multimap_int32) { MultiMapTest<int32_t>(); }
    TEST(Btree, multimap_int64) { MultiMapTest<int64_t>(); }
    TEST(Btree, multimap_string) { MultiMapTest<std::string>(); }
    TEST(Btree, multimap_pair) { MultiMapTest<std::pair<int, int>>(); }

    struct CompareIntToString {
        bool operator()(const std::string &a, const std::string &b) const {
            return a < b;
        }
        bool operator()(const std::string &a, int b) const {
            return a < std::to_string(b);
        }
        bool operator()(int a, const std::string &b) const {
            return std::to_string(a) < b;
        }
        using is_transparent = void;
    };

    struct NonTransparentCompare {
        template <typename T, typename U>
        bool operator()(const T& t, const U& u) const {
            // Treating all comparators as transparent can cause inefficiencies (see
            // N3657 C++ proposal). Test that for comparators without 'is_transparent'
            // alias (like this one), we do not attempt heterogeneous lookup.
            EXPECT_TRUE((std::is_same<T, U>()));
            return t < u;
        }
    };

    template <typename T>
    bool CanEraseWithEmptyBrace(T t, decltype(t.erase({})) *) {
        return true;
    }

    template <typename T>
    bool CanEraseWithEmptyBrace(T, ...) {
        return false;
    }

    template <typename T>
    void TestHeterogeneous(T table) {
        auto lb = table.lower_bound("3");
        EXPECT_EQ(lb, table.lower_bound(3));
        EXPECT_NE(lb, table.lower_bound(4));
        EXPECT_EQ(lb, table.lower_bound({"3"}));
        EXPECT_NE(lb, table.lower_bound({}));

        auto ub = table.upper_bound("3");
        EXPECT_EQ(ub, table.upper_bound(3));
        EXPECT_NE(ub, table.upper_bound(5));
        EXPECT_EQ(ub, table.upper_bound({"3"}));
        EXPECT_NE(ub, table.upper_bound({}));

        auto er = table.equal_range("3");
        EXPECT_EQ(er, table.equal_range(3));
        EXPECT_NE(er, table.equal_range(4));
        EXPECT_EQ(er, table.equal_range({"3"}));
        EXPECT_NE(er, table.equal_range({}));

        auto it = table.find("3");
        EXPECT_EQ(it, table.find(3));
        EXPECT_NE(it, table.find(4));
        EXPECT_EQ(it, table.find({"3"}));
        EXPECT_NE(it, table.find({}));

        EXPECT_TRUE(table.contains(3));
        EXPECT_FALSE(table.contains(4));
        EXPECT_TRUE(table.count({"3"}));
        EXPECT_FALSE(table.contains({}));

        EXPECT_EQ(1, table.count(3));
        EXPECT_EQ(0, table.count(4));
        EXPECT_EQ(1, table.count({"3"}));
        EXPECT_EQ(0, table.count({}));

        auto copy = table;
        copy.erase(3);
        EXPECT_EQ(table.size() - 1, copy.size());
        copy.erase(4);
        EXPECT_EQ(table.size() - 1, copy.size());
        copy.erase({"5"});
        EXPECT_EQ(table.size() - 2, copy.size());
        EXPECT_FALSE(CanEraseWithEmptyBrace(table, nullptr));

        // Also run it with const T&.
        if (std::is_class<T>()) TestHeterogeneous<const T &>(table);
    }

    TEST(Btree, HeterogeneousLookup) {
        TestHeterogeneous(btree_set<std::string, CompareIntToString>{"1", "3", "5"});
        TestHeterogeneous(btree_map<std::string, int, CompareIntToString>{
                {"1", 1}, {"3", 3}, {"5", 5}});
        TestHeterogeneous(
            btree_multiset<std::string, CompareIntToString>{"1", "3", "5"});
        TestHeterogeneous(btree_multimap<std::string, int, CompareIntToString>{
                {"1", 1}, {"3", 3}, {"5", 5}});

        // Only maps have .at()
        btree_map<std::string, int, CompareIntToString> map{
            {"", -1}, {"1", 1}, {"3", 3}, {"5", 5}};
        EXPECT_EQ(1, map.at(1));
        EXPECT_EQ(3, map.at({"3"}));
        EXPECT_EQ(-1, map.at({}));
        const auto &cmap = map;
        EXPECT_EQ(1, cmap.at(1));
        EXPECT_EQ(3, cmap.at({"3"}));
        EXPECT_EQ(-1, cmap.at({}));
    }

    TEST(Btree, NoHeterogeneousLookupWithoutAlias) {
        using StringSet = phmap::btree_set<std::string, NonTransparentCompare>;
        StringSet s;
        ASSERT_TRUE(s.insert("hello").second);
        ASSERT_TRUE(s.insert("world").second);
        EXPECT_TRUE(s.end() == s.find("blah"));
        EXPECT_TRUE(s.begin() == s.lower_bound("hello"));
        EXPECT_EQ(1, s.count("world"));
        EXPECT_TRUE(s.contains("hello"));
        EXPECT_TRUE(s.contains("world"));
        EXPECT_FALSE(s.contains("blah"));

        using StringMultiSet =
            phmap::btree_multiset<std::string, NonTransparentCompare>;
        StringMultiSet ms;
        ms.insert("hello");
        ms.insert("world");
        ms.insert("world");
        EXPECT_TRUE(ms.end() == ms.find("blah"));
        EXPECT_TRUE(ms.begin() == ms.lower_bound("hello"));
        EXPECT_EQ(2, ms.count("world"));
        EXPECT_TRUE(ms.contains("hello"));
        EXPECT_TRUE(ms.contains("world"));
        EXPECT_FALSE(ms.contains("blah"));
    }

    TEST(Btree, DefaultTransparent) {
        {
            // `int` does not have a default transparent comparator.
            // The input value is converted to key_type.
            btree_set<int> s = {1};
            double d = 1.1;
            EXPECT_EQ(s.begin(), s.find(d));
            EXPECT_TRUE(s.contains(d));
        }

        {
            // `std::string` has heterogeneous support.
            btree_set<std::string> s = {"A"};
#if PHMAP_HAVE_STD_STRING_VIEW
            EXPECT_EQ(s.begin(), s.find(std::string_view("A")));
            EXPECT_TRUE(s.contains(std::string_view("A")));
#endif
        }
    }

    class StringLike {
    public:
        StringLike() = default;

        StringLike(const char* s) : s_(s) {  // NOLINT
            ++constructor_calls_;
        }

        bool operator<(const StringLike& a) const {
            return s_ < a.s_;
        }

        static void clear_constructor_call_count() {
            constructor_calls_ = 0;
        }

        static int constructor_calls() {
            return constructor_calls_;
        }

    private:
        static int constructor_calls_;
        std::string s_;
    };

    int StringLike::constructor_calls_ = 0;

    TEST(Btree, HeterogeneousLookupDoesntDegradePerformance) {
        using StringSet = phmap::btree_set<StringLike>;
        StringSet s;
        for (int i = 0; i < 100; ++i) {
            ASSERT_TRUE(s.insert(std::to_string(i).c_str()).second);
        }
        StringLike::clear_constructor_call_count();
        s.find("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.contains("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.count("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.lower_bound("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.upper_bound("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.equal_range("50");
        ASSERT_EQ(1, StringLike::constructor_calls());

        StringLike::clear_constructor_call_count();
        s.erase("50");
        ASSERT_EQ(1, StringLike::constructor_calls());
    }

    // Verify that swapping btrees swaps the key comparison functors and that we can
    // use non-default constructible comparators.
    struct SubstringLess {
        SubstringLess() = delete;
        explicit SubstringLess(int length) : n(length) {}
        bool operator()(const std::string &a, const std::string &b) const {
#if PHMAP_HAVE_STD_STRING_VIEW
            return std::string_view(a).substr(0, n) <
                std::string_view(b).substr(0, n);
#else
            return a.substr(0, n) < b.substr(0, n);
#endif
        }
        int n;
    };

    TEST(Btree, SwapKeyCompare) {
        using SubstringSet = phmap::btree_set<std::string, SubstringLess>;
        SubstringSet s1(SubstringLess(1), SubstringSet::allocator_type());
        SubstringSet s2(SubstringLess(2), SubstringSet::allocator_type());

        ASSERT_TRUE(s1.insert("a").second);
        ASSERT_FALSE(s1.insert("aa").second);

        ASSERT_TRUE(s2.insert("a").second);
        ASSERT_TRUE(s2.insert("aa").second);
        ASSERT_FALSE(s2.insert("aaa").second);

        swap(s1, s2);

        ASSERT_TRUE(s1.insert("b").second);
        ASSERT_TRUE(s1.insert("bb").second);
        ASSERT_FALSE(s1.insert("bbb").second);

        ASSERT_TRUE(s2.insert("b").second);
        ASSERT_FALSE(s2.insert("bb").second);
    }

    TEST(Btree, UpperBoundRegression) {
        // Regress a bug where upper_bound would default-construct a new key_compare
        // instead of copying the existing one.
        using SubstringSet = phmap::btree_set<std::string, SubstringLess>;
        SubstringSet my_set(SubstringLess(3));
        my_set.insert("aab");
        my_set.insert("abb");
        // We call upper_bound("aaa").  If this correctly uses the length 3
        // comparator, aaa < aab < abb, so we should get aab as the result.
        // If it instead uses the default-constructed length 2 comparator,
        // aa == aa < ab, so we'll get abb as our result.
        SubstringSet::iterator it = my_set.upper_bound("aaa");
        ASSERT_TRUE(it != my_set.end());
        EXPECT_EQ("aab", *it);
    }

    TEST(Btree, Comparison) {
        const int kSetSize = 1201;
        phmap::btree_set<int64_t> my_set;
        for (int i = 0; i < kSetSize; ++i) {
            my_set.insert(i);
        }
        phmap::btree_set<int64_t> my_set_copy(my_set);
        EXPECT_TRUE(my_set_copy == my_set);
        EXPECT_TRUE(my_set == my_set_copy);
        EXPECT_FALSE(my_set_copy != my_set);
        EXPECT_FALSE(my_set != my_set_copy);

        my_set.insert(kSetSize);
        EXPECT_FALSE(my_set_copy == my_set);
        EXPECT_FALSE(my_set == my_set_copy);
        EXPECT_TRUE(my_set_copy != my_set);
        EXPECT_TRUE(my_set != my_set_copy);

        my_set.erase(kSetSize - 1);
        EXPECT_FALSE(my_set_copy == my_set);
        EXPECT_FALSE(my_set == my_set_copy);
        EXPECT_TRUE(my_set_copy != my_set);
        EXPECT_TRUE(my_set != my_set_copy);

        phmap::btree_map<std::string, int64_t> my_map;
        for (int i = 0; i < kSetSize; ++i) {
            my_map[std::string(i, 'a')] = i;
        }
        phmap::btree_map<std::string, int64_t> my_map_copy(my_map);
        EXPECT_TRUE(my_map_copy == my_map);
        EXPECT_TRUE(my_map == my_map_copy);
        EXPECT_FALSE(my_map_copy != my_map);
        EXPECT_FALSE(my_map != my_map_copy);

        ++my_map_copy[std::string(7, 'a')];
        EXPECT_FALSE(my_map_copy == my_map);
        EXPECT_FALSE(my_map == my_map_copy);
        EXPECT_TRUE(my_map_copy != my_map);
        EXPECT_TRUE(my_map != my_map_copy);

        my_map_copy = my_map;
        my_map["hello"] = kSetSize;
        EXPECT_FALSE(my_map_copy == my_map);
        EXPECT_FALSE(my_map == my_map_copy);
        EXPECT_TRUE(my_map_copy != my_map);
        EXPECT_TRUE(my_map != my_map_copy);

        my_map.erase(std::string(kSetSize - 1, 'a'));
        EXPECT_FALSE(my_map_copy == my_map);
        EXPECT_FALSE(my_map == my_map_copy);
        EXPECT_TRUE(my_map_copy != my_map);
        EXPECT_TRUE(my_map != my_map_copy);
    }

    TEST(Btree, RangeCtorSanity) {
        std::vector<int> ivec;
        ivec.push_back(1);
        std::map<int, int> imap;
        imap.insert(std::make_pair(1, 2));
        phmap::btree_multiset<int> tmset(ivec.begin(), ivec.end());
        phmap::btree_multimap<int, int> tmmap(imap.begin(), imap.end());
        phmap::btree_set<int> tset(ivec.begin(), ivec.end());
        phmap::btree_map<int, int> tmap(imap.begin(), imap.end());
        EXPECT_EQ(1, tmset.size());
        EXPECT_EQ(1, tmmap.size());
        EXPECT_EQ(1, tset.size());
        EXPECT_EQ(1, tmap.size());
    }

    TEST(Btree, BtreeMapCanHoldMoveOnlyTypes) {
        phmap::btree_map<std::string, std::unique_ptr<std::string>> m;

        std::unique_ptr<std::string> &v = m["A"];
        EXPECT_TRUE(v == nullptr);
        v.reset(new std::string("X"));

        auto iter = m.find("A");
        EXPECT_EQ("X", *iter->second);
    }

    TEST(Btree, InitializerListConstructor) {
        phmap::btree_set<std::string> set({"a", "b"});
        EXPECT_EQ(set.count("a"), 1);
        EXPECT_EQ(set.count("b"), 1);

        phmap::btree_multiset<int> mset({1, 1, 4});
        EXPECT_EQ(mset.count(1), 2);
        EXPECT_EQ(mset.count(4), 1);

        phmap::btree_map<int, int> map({{1, 5}, {2, 10}});
        EXPECT_EQ(map[1], 5);
        EXPECT_EQ(map[2], 10);

        phmap::btree_multimap<int, int> mmap({{1, 5}, {1, 10}});
        auto range = mmap.equal_range(1);
        auto it = range.first;
        ASSERT_NE(it, range.second);
        EXPECT_EQ(it->second, 5);
        ASSERT_NE(++it, range.second);
        EXPECT_EQ(it->second, 10);
        EXPECT_EQ(++it, range.second);
    }

    TEST(Btree, InitializerListInsert) {
        phmap::btree_set<std::string> set;
        set.insert({"a", "b"});
        EXPECT_EQ(set.count("a"), 1);
        EXPECT_EQ(set.count("b"), 1);

        phmap::btree_multiset<int> mset;
        mset.insert({1, 1, 4});
        EXPECT_EQ(mset.count(1), 2);
        EXPECT_EQ(mset.count(4), 1);

        phmap::btree_map<int, int> map;
        map.insert({{1, 5}, {2, 10}});
        // Test that inserting one element using an initializer list also works.
        map.insert({3, 15});
        EXPECT_EQ(map[1], 5);
        EXPECT_EQ(map[2], 10);
        EXPECT_EQ(map[3], 15);

        phmap::btree_multimap<int, int> mmap;
        mmap.insert({{1, 5}, {1, 10}});
        auto range = mmap.equal_range(1);
        auto it = range.first;
        ASSERT_NE(it, range.second);
        EXPECT_EQ(it->second, 5);
        ASSERT_NE(++it, range.second);
        EXPECT_EQ(it->second, 10);
        EXPECT_EQ(++it, range.second);
    }

    template <typename Compare, typename K>
    void AssertKeyCompareToAdapted() {
        using Adapted = typename key_compare_to_adapter<Compare>::type;
        static_assert(!std::is_same<Adapted, Compare>::value,
                      "key_compare_to_adapter should have adapted this comparator.");
        static_assert(
            std::is_same<phmap::weak_ordering,
            phmap::invoke_result_t<Adapted, const K &, const K &>>::value,
            "Adapted comparator should be a key-compare-to comparator.");
    }
    template <typename Compare, typename K>
    void AssertKeyCompareToNotAdapted() {
        using Unadapted = typename key_compare_to_adapter<Compare>::type;
        static_assert(
            std::is_same<Unadapted, Compare>::value,
            "key_compare_to_adapter shouldn't have adapted this comparator.");
        static_assert(
            std::is_same<bool,
            phmap::invoke_result_t<Unadapted, const K &, const K &>>::value,
            "Un-adapted comparator should return bool.");
    }

    TEST(Btree, KeyCompareToAdapter) {
        AssertKeyCompareToAdapted<std::less<std::string>, std::string>();
        AssertKeyCompareToAdapted<std::greater<std::string>, std::string>();
#if PHMAP_HAVE_STD_STRING_VIEW
        AssertKeyCompareToAdapted<std::less<std::string_view>, std::string_view>();
        AssertKeyCompareToAdapted<std::greater<std::string_view>,
                                  std::string_view>();
#endif
        AssertKeyCompareToNotAdapted<std::less<int>, int>();
        AssertKeyCompareToNotAdapted<std::greater<int>, int>();
    }

    TEST(Btree, RValueInsert) {
        InstanceTracker tracker;

        phmap::btree_set<MovableOnlyInstance> set;
        set.insert(MovableOnlyInstance(1));
        set.insert(MovableOnlyInstance(3));
        MovableOnlyInstance two(2);
        set.insert(set.find(MovableOnlyInstance(3)), std::move(two));
        auto it = set.find(MovableOnlyInstance(2));
        ASSERT_NE(it, set.end());
        ASSERT_NE(++it, set.end());
        EXPECT_EQ(it->value(), 3);

        phmap::btree_multiset<MovableOnlyInstance> mset;
        MovableOnlyInstance zero(0);
        MovableOnlyInstance zero2(0);
        mset.insert(std::move(zero));
        mset.insert(mset.find(MovableOnlyInstance(0)), std::move(zero2));
        EXPECT_EQ(mset.count(MovableOnlyInstance(0)), 2);

        phmap::btree_map<int, MovableOnlyInstance> map;
        std::pair<const int, MovableOnlyInstance> p1 = {1, MovableOnlyInstance(5)};
        std::pair<const int, MovableOnlyInstance> p2 = {2, MovableOnlyInstance(10)};
        std::pair<const int, MovableOnlyInstance> p3 = {3, MovableOnlyInstance(15)};
        map.insert(std::move(p1));
        map.insert(std::move(p3));
        map.insert(map.find(3), std::move(p2));
        ASSERT_NE(map.find(2), map.end());
        EXPECT_EQ(map.find(2)->second.value(), 10);

        phmap::btree_multimap<int, MovableOnlyInstance> mmap;
        std::pair<const int, MovableOnlyInstance> p4 = {1, MovableOnlyInstance(5)};
        std::pair<const int, MovableOnlyInstance> p5 = {1, MovableOnlyInstance(10)};
        mmap.insert(std::move(p4));
        mmap.insert(mmap.find(1), std::move(p5));
        auto range = mmap.equal_range(1);
        auto it1 = range.first;
        ASSERT_NE(it1, range.second);
        EXPECT_EQ(it1->second.value(), 10);
        ASSERT_NE(++it1, range.second);
        EXPECT_EQ(it1->second.value(), 5);
        EXPECT_EQ(++it1, range.second);

        EXPECT_EQ(tracker.copies(), 0);
        EXPECT_EQ(tracker.swaps(), 0);
    }

}  // namespace

class BtreeNodePeer {
public:
    // Yields the size of a leaf node with a specific number of values.
    template <typename ValueType>
    constexpr static size_t GetTargetNodeSize(size_t target_values_per_node) {
        return btree_node<
            set_params<ValueType, std::less<ValueType>, std::allocator<ValueType>,
                       /*TargetNodeSize=*/256,  // This parameter isn't used here.
                       /*Multi=*/false>>::SizeWithNValues(target_values_per_node);
    }

    // Yields the number of values in a (non-root) leaf node for this set.
    template <typename Set>
    constexpr static size_t GetNumValuesPerNode() {
        return btree_node<typename Set::params_type>::kNodeValues;
    }
};

namespace {

    // A btree set with a specific number of values per node.
    template <typename Key, int TargetValuesPerNode, typename Cmp = std::less<Key>>
        class SizedBtreeSet
        : public btree_set_container<btree<
                                         set_params<Key, Cmp, std::allocator<Key>,
                                                    BtreeNodePeer::GetTargetNodeSize<Key>(TargetValuesPerNode),
                                                    /*Multi=*/false>>> {
        using Base = typename SizedBtreeSet::btree_set_container;

    public:
        SizedBtreeSet() {}
        using Base::Base;
    };

    template <typename Set>
    void ExpectOperationCounts(const int expected_moves,
                               const int expected_comparisons,
                               const std::vector<int> &values,
                               InstanceTracker *tracker, Set *set) {
        for (const int v : values) set->insert(MovableOnlyInstance(v));
        set->clear();
        EXPECT_EQ(tracker->moves(), expected_moves);
        EXPECT_EQ(tracker->comparisons(), expected_comparisons);
        EXPECT_EQ(tracker->copies(), 0);
        EXPECT_EQ(tracker->swaps(), 0);
        tracker->ResetCopiesMovesSwaps();
    }

    // Note: when the values in this test change, it is expected to have an impact
    // on performance.
    TEST(Btree, MovesComparisonsCopiesSwapsTracking) {
        InstanceTracker tracker;
        // Note: this is minimum number of values per node.
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/3> set3;
        // Note: this is the default number of values per node for a set of int32s
        // (with 64-bit pointers).
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/61> set61;
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/100> set100;

        // Don't depend on flags for random values because then the expectations will
        // fail if the flags change.
        std::vector<int> values =
            GenerateValuesWithSeed<int>(10000, 1 << 22, /*seed=*/23);

        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set3)>(), 3);
        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>(), 61);
        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set100)>(), 100);
        PHMAP_IF_CONSTEXPR (sizeof(void *) == 8) {
            EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<phmap::btree_set<int32_t>>(),
                      BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>());
        }

        // Test key insertion/deletion in random order.
        ExpectOperationCounts(45281, 132551, values, &tracker, &set3);
        ExpectOperationCounts(386718, 129807, values, &tracker, &set61);
        ExpectOperationCounts(586761, 130310, values, &tracker, &set100);

        // Test key insertion/deletion in sorted order.
        std::sort(values.begin(), values.end());
        ExpectOperationCounts(26638, 92134, values, &tracker, &set3);
        ExpectOperationCounts(20208, 87757, values, &tracker, &set61);
        ExpectOperationCounts(20124, 96583, values, &tracker, &set100);

        // Test key insertion/deletion in reverse sorted order.
        std::reverse(values.begin(), values.end());
        ExpectOperationCounts(49951, 119325, values, &tracker, &set3);
        ExpectOperationCounts(338813, 118266, values, &tracker, &set61);
        ExpectOperationCounts(534529, 125279, values, &tracker, &set100);
    }

    struct MovableOnlyInstanceThreeWayCompare {
        phmap::weak_ordering operator()(const MovableOnlyInstance &a,
                                        const MovableOnlyInstance &b) const {
            return a.compare(b);
        }
    };

    // Note: when the values in this test change, it is expected to have an impact
    // on performance.
    TEST(Btree, MovesComparisonsCopiesSwapsTrackingThreeWayCompare) {
        InstanceTracker tracker;
        // Note: this is minimum number of values per node.
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/3,
                      MovableOnlyInstanceThreeWayCompare>
            set3;
        // Note: this is the default number of values per node for a set of int32s
        // (with 64-bit pointers).
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/61,
                      MovableOnlyInstanceThreeWayCompare>
            set61;
        SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/100,
                      MovableOnlyInstanceThreeWayCompare>
            set100;

        // Don't depend on flags for random values because then the expectations will
        // fail if the flags change.
        std::vector<int> values =
            GenerateValuesWithSeed<int>(10000, 1 << 22, /*seed=*/23);

        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set3)>(), 3);
        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>(), 61);
        EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set100)>(), 100);
        PHMAP_IF_CONSTEXPR (sizeof(void *) == 8) {
            EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<phmap::btree_set<int32_t>>(),
                      BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>());
        }

        // Test key insertion/deletion in random order.
        ExpectOperationCounts(45281, 122560, values, &tracker, &set3);
        ExpectOperationCounts(386718, 119816, values, &tracker, &set61);
        ExpectOperationCounts(586761, 120319, values, &tracker, &set100);

        // Test key insertion/deletion in sorted order.
        std::sort(values.begin(), values.end());
        ExpectOperationCounts(26638, 92134, values, &tracker, &set3);
        ExpectOperationCounts(20208, 87757, values, &tracker, &set61);
        ExpectOperationCounts(20124, 96583, values, &tracker, &set100);

        // Test key insertion/deletion in reverse sorted order.
        std::reverse(values.begin(), values.end());
        ExpectOperationCounts(49951, 109326, values, &tracker, &set3);
        ExpectOperationCounts(338813, 108267, values, &tracker, &set61);
        ExpectOperationCounts(534529, 115280, values, &tracker, &set100);
    }

    struct NoDefaultCtor {
        int num;
        explicit NoDefaultCtor(int i) : num(i) {}

        friend bool operator<(const NoDefaultCtor& a, const NoDefaultCtor& b) {
            return a.num < b.num;
        }
    };

    TEST(Btree, BtreeMapCanHoldNoDefaultCtorTypes) {
        phmap::btree_map<NoDefaultCtor, NoDefaultCtor> m;

        for (int i = 1; i <= 99; ++i) {
            SCOPED_TRACE(i);
            EXPECT_TRUE(m.emplace(NoDefaultCtor(i), NoDefaultCtor(100 - i)).second);
        }
        EXPECT_FALSE(m.emplace(NoDefaultCtor(78), NoDefaultCtor(0)).second);

        auto iter99 = m.find(NoDefaultCtor(99));
        ASSERT_NE(iter99, m.end());
        EXPECT_EQ(iter99->second.num, 1);

        auto iter1 = m.find(NoDefaultCtor(1));
        ASSERT_NE(iter1, m.end());
        EXPECT_EQ(iter1->second.num, 99);

        auto iter50 = m.find(NoDefaultCtor(50));
        ASSERT_NE(iter50, m.end());
        EXPECT_EQ(iter50->second.num, 50);

        auto iter25 = m.find(NoDefaultCtor(25));
        ASSERT_NE(iter25, m.end());
        EXPECT_EQ(iter25->second.num, 75);
    }

    TEST(Btree, BtreeMultimapCanHoldNoDefaultCtorTypes) {
        phmap::btree_multimap<NoDefaultCtor, NoDefaultCtor> m;

        for (int i = 1; i <= 99; ++i) {
            SCOPED_TRACE(i);
            m.emplace(NoDefaultCtor(i), NoDefaultCtor(100 - i));
        }

        auto iter99 = m.find(NoDefaultCtor(99));
        ASSERT_NE(iter99, m.end());
        EXPECT_EQ(iter99->second.num, 1);

        auto iter1 = m.find(NoDefaultCtor(1));
        ASSERT_NE(iter1, m.end());
        EXPECT_EQ(iter1->second.num, 99);

        auto iter50 = m.find(NoDefaultCtor(50));
        ASSERT_NE(iter50, m.end());
        EXPECT_EQ(iter50->second.num, 50);

        auto iter25 = m.find(NoDefaultCtor(25));
        ASSERT_NE(iter25, m.end());
        EXPECT_EQ(iter25->second.num, 75);
    }

    TEST(Btree, MapAt) {
        phmap::btree_map<int, int> map = {{1, 2}, {2, 4}};
        EXPECT_EQ(map.at(1), 2);
        EXPECT_EQ(map.at(2), 4);
        map.at(2) = 8;
        const phmap::btree_map<int, int> &const_map = map;
        EXPECT_EQ(const_map.at(1), 2);
        EXPECT_EQ(const_map.at(2), 8);
#ifdef PHMAP_HAVE_EXCEPTIONS
        EXPECT_THROW(map.at(3), std::out_of_range);
#else
        EXPECT_DEATH(map.at(3), "phmap::btree_map::at");
#endif
    }

    TEST(Btree, BtreeMultisetEmplace) {
        const int value_to_insert = 123456;
        phmap::btree_multiset<int> s;
        auto iter = s.emplace(value_to_insert);
        ASSERT_NE(iter, s.end());
        EXPECT_EQ(*iter, value_to_insert);
        auto iter2 = s.emplace(value_to_insert);
        EXPECT_NE(iter2, iter);
        ASSERT_NE(iter2, s.end());
        EXPECT_EQ(*iter2, value_to_insert);
        auto result = s.equal_range(value_to_insert);
        EXPECT_EQ(std::distance(result.first, result.second), 2);
    }

    TEST(Btree, BtreeMultisetEmplaceHint) {
        const int value_to_insert = 123456;
        phmap::btree_multiset<int> s;
        auto iter = s.emplace(value_to_insert);
        ASSERT_NE(iter, s.end());
        EXPECT_EQ(*iter, value_to_insert);
        auto emplace_iter = s.emplace_hint(iter, value_to_insert);
        EXPECT_NE(emplace_iter, iter);
        ASSERT_NE(emplace_iter, s.end());
        EXPECT_EQ(*emplace_iter, value_to_insert);
    }

    TEST(Btree, BtreeMultimapEmplace) {
        const int key_to_insert = 123456;
        const char value0[] = "a";
        phmap::btree_multimap<int, std::string> s;
        auto iter = s.emplace(key_to_insert, value0);
        ASSERT_NE(iter, s.end());
        EXPECT_EQ(iter->first, key_to_insert);
        EXPECT_EQ(iter->second, value0);
        const char value1[] = "b";
        auto iter2 = s.emplace(key_to_insert, value1);
        EXPECT_NE(iter2, iter);
        ASSERT_NE(iter2, s.end());
        EXPECT_EQ(iter2->first, key_to_insert);
        EXPECT_EQ(iter2->second, value1);
        auto result = s.equal_range(key_to_insert);
        EXPECT_EQ(std::distance(result.first, result.second), 2);
    }

    TEST(Btree, BtreeMultimapEmplaceHint) {
        const int key_to_insert = 123456;
        const char value0[] = "a";
        phmap::btree_multimap<int, std::string> s;
        auto iter = s.emplace(key_to_insert, value0);
        ASSERT_NE(iter, s.end());
        EXPECT_EQ(iter->first, key_to_insert);
        EXPECT_EQ(iter->second, value0);
        const char value1[] = "b";
        auto emplace_iter = s.emplace_hint(iter, key_to_insert, value1);
        EXPECT_NE(emplace_iter, iter);
        ASSERT_NE(emplace_iter, s.end());
        EXPECT_EQ(emplace_iter->first, key_to_insert);
        EXPECT_EQ(emplace_iter->second, value1);
    }

    TEST(Btree, ConstIteratorAccessors) {
        phmap::btree_set<int> set;
        for (int i = 0; i < 100; ++i) {
            set.insert(i);
        }

        auto it = set.cbegin();
        auto r_it = set.crbegin();
        for (int i = 0; i < 100; ++i, ++it, ++r_it) {
            ASSERT_EQ(*it, i);
            ASSERT_EQ(*r_it, 99 - i);
        }
        EXPECT_EQ(it, set.cend());
        EXPECT_EQ(r_it, set.crend());
    }

#if 0
    TEST(Btree, StrSplitCompatible) {
        const phmap::btree_set<std::string> split_set = phmap::StrSplit("a,b,c", ',');
        const phmap::btree_set<std::string> expected_set = {"a", "b", "c"};

        EXPECT_EQ(split_set, expected_set);
    }
#endif

    // We can't use EXPECT_EQ/etc. to compare phmap::weak_ordering because they
    // convert literal 0 to int and phmap::weak_ordering can only be compared with
    // literal 0. Defining this function allows for avoiding ClangTidy warnings.
    bool Identity(const bool b) { return b; }

    TEST(Btree, ValueComp) {
        phmap::btree_set<int> s;
        EXPECT_TRUE(s.value_comp()(1, 2));
        EXPECT_FALSE(s.value_comp()(2, 2));
        EXPECT_FALSE(s.value_comp()(2, 1));

        phmap::btree_map<int, int> m1;
        EXPECT_TRUE(m1.value_comp()(std::make_pair(1, 0), std::make_pair(2, 0)));
        EXPECT_FALSE(m1.value_comp()(std::make_pair(2, 0), std::make_pair(2, 0)));
        EXPECT_FALSE(m1.value_comp()(std::make_pair(2, 0), std::make_pair(1, 0)));

        phmap::btree_map<std::string, int> m2;
        EXPECT_TRUE(Identity(
                        m2.value_comp()(std::make_pair("a", 0), std::make_pair("b", 0)) < 0));
        EXPECT_TRUE(Identity(
                        m2.value_comp()(std::make_pair("b", 0), std::make_pair("b", 0)) == 0));
        EXPECT_TRUE(Identity(
                        m2.value_comp()(std::make_pair("b", 0), std::make_pair("a", 0)) > 0));
    }

    TEST(Btree, DefaultConstruction) {
        phmap::btree_set<int> s;
        phmap::btree_map<int, int> m;
        phmap::btree_multiset<int> ms;
        phmap::btree_multimap<int, int> mm;

        EXPECT_TRUE(s.empty());
        EXPECT_TRUE(m.empty());
        EXPECT_TRUE(ms.empty());
        EXPECT_TRUE(mm.empty());
    }

#if 0
    TEST(Btree, SwissTableHashable) {
        static constexpr int kValues = 10000;
        std::vector<int> values(kValues);
        std::iota(values.begin(), values.end(), 0);
        std::vector<std::pair<int, int>> map_values;
        for (int v : values) map_values.emplace_back(v, -v);

        using set = phmap::btree_set<int>;
        EXPECT_TRUE(phmap::VerifyTypeImplementsPhmapHashCorrectly({
                    set{},
                        set{1},
                            set{2},
                                set{1, 2},
                                    set{2, 1},
                                        set(values.begin(), values.end()),
                                            set(values.rbegin(), values.rend()),
                                            }));

        using mset = phmap::btree_multiset<int>;
        EXPECT_TRUE(phmap::VerifyTypeImplementsPhmapHashCorrectly({
                    mset{},
                        mset{1},
                            mset{1, 1},
                                mset{2},
                                    mset{2, 2},
                                        mset{1, 2},
                                            mset{1, 1, 2},
                                                mset{1, 2, 2},
                                                    mset{1, 1, 2, 2},
                                                        mset(values.begin(), values.end()),
                                                            mset(values.rbegin(), values.rend()),
                                                            }));

        using map = phmap::btree_map<int, int>;
        EXPECT_TRUE(phmap::VerifyTypeImplementsPhmapHashCorrectly({
                    map{},
                        map{{1, 0}},
                            map{{1, 1}},
                                map{{2, 0}},
                                    map{{2, 2}},
                                        map{{1, 0}, {2, 1}},
                                            map(map_values.begin(), map_values.end()),
                                                map(map_values.rbegin(), map_values.rend()),
                                                }));

        using mmap = phmap::btree_multimap<int, int>;
        EXPECT_TRUE(phmap::VerifyTypeImplementsPhmapHashCorrectly({
                    mmap{},
                        mmap{{1, 0}},
                            mmap{{1, 1}},
                                mmap{{1, 0}, {1, 1}},
                                    mmap{{1, 1}, {1, 0}},
                                        mmap{{2, 0}},
                                            mmap{{2, 2}},
                                                mmap{{1, 0}, {2, 1}},
                                                    mmap(map_values.begin(), map_values.end()),
                                                        mmap(map_values.rbegin(), map_values.rend()),
                                                        }));
    }
#endif

    TEST(Btree, ComparableSet) {
        phmap::btree_set<int> s1 = {1, 2};
        phmap::btree_set<int> s2 = {2, 3};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_LE(s1, s1);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
        EXPECT_GE(s1, s1);
    }

    TEST(Btree, ComparableSetsDifferentLength) {
        phmap::btree_set<int> s1 = {1, 2};
        phmap::btree_set<int> s2 = {1, 2, 3};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
    }

    TEST(Btree, ComparableMultiset) {
        phmap::btree_multiset<int> s1 = {1, 2};
        phmap::btree_multiset<int> s2 = {2, 3};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_LE(s1, s1);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
        EXPECT_GE(s1, s1);
    }

    TEST(Btree, ComparableMap) {
        phmap::btree_map<int, int> s1 = {{1, 2}};
        phmap::btree_map<int, int> s2 = {{2, 3}};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_LE(s1, s1);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
        EXPECT_GE(s1, s1);
    }

    TEST(Btree, ComparableMultimap) {
        phmap::btree_multimap<int, int> s1 = {{1, 2}};
        phmap::btree_multimap<int, int> s2 = {{2, 3}};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_LE(s1, s1);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
        EXPECT_GE(s1, s1);
    }

    TEST(Btree, ComparableSetWithCustomComparator) {
        // As specified by
        // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf section
        // [container.requirements.general].12, ordering associative containers always
        // uses default '<' operator
        // - even if otherwise the container uses custom functor.
        phmap::btree_set<int, std::greater<int>> s1 = {1, 2};
        phmap::btree_set<int, std::greater<int>> s2 = {2, 3};
        EXPECT_LT(s1, s2);
        EXPECT_LE(s1, s2);
        EXPECT_LE(s1, s1);
        EXPECT_GT(s2, s1);
        EXPECT_GE(s2, s1);
        EXPECT_GE(s1, s1);
    }

    TEST(Btree, EraseReturnsIterator) {
        phmap::btree_set<int> set = {1, 2, 3, 4, 5};
        auto result_it = set.erase(set.begin(), set.find(3));
        EXPECT_EQ(result_it, set.find(3));
        result_it = set.erase(set.find(5));
        EXPECT_EQ(result_it, set.end());
    }

    TEST(Btree, ExtractAndInsertNodeHandleSet) {
        phmap::btree_set<int> src1 = {1, 2, 3, 4, 5};
        auto nh = src1.extract(src1.find(3));
        EXPECT_THAT(src1, ElementsAre(1, 2, 4, 5));
        phmap::btree_set<int> other;
        phmap::btree_set<int>::insert_return_type res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(3));
        EXPECT_EQ(res.position, other.find(3));
        EXPECT_TRUE(res.inserted);
        EXPECT_TRUE(res.node.empty());

        phmap::btree_set<int> src2 = {3, 4};
        nh = src2.extract(src2.find(3));
        EXPECT_THAT(src2, ElementsAre(4));
        res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(3));
        EXPECT_EQ(res.position, other.find(3));
        EXPECT_FALSE(res.inserted);
        ASSERT_FALSE(res.node.empty());
        EXPECT_EQ(res.node.value(), 3);
    }

    template <typename Set>
    void TestExtractWithTrackingForSet() {
        InstanceTracker tracker;
        {
            Set s;
            // Add enough elements to make sure we test internal nodes too.
            const size_t kSize = 1000;
            while (s.size() < kSize) {
                s.insert(MovableOnlyInstance(s.size()));
            }
            for (size_t i = 0; i < kSize; ++i) {
                // Extract with key
                auto nh = s.extract(MovableOnlyInstance(i));
                EXPECT_EQ(s.size(), kSize - 1);
                EXPECT_EQ(nh.value().value(), i);
                // Insert with node
                s.insert(std::move(nh));
                EXPECT_EQ(s.size(), kSize);

                // Extract with iterator
                auto it = s.find(MovableOnlyInstance(i));
                nh = s.extract(it);
                EXPECT_EQ(s.size(), kSize - 1);
                EXPECT_EQ(nh.value().value(), i);
                // Insert with node and hint
                s.insert(s.begin(), std::move(nh));
                EXPECT_EQ(s.size(), kSize);
            }
        }
        EXPECT_EQ(0, tracker.instances());
    }

    template <typename Map>
    void TestExtractWithTrackingForMap() {
        InstanceTracker tracker;
        {
            Map m;
            // Add enough elements to make sure we test internal nodes too.
            const size_t kSize = 1000;
            while (m.size() < kSize) {
                m.insert(
                    {CopyableMovableInstance(m.size()), MovableOnlyInstance(m.size())});
            }
            for (size_t i = 0; i < kSize; ++i) {
                // Extract with key
                auto nh = m.extract(CopyableMovableInstance(i));
                EXPECT_EQ(m.size(), kSize - 1);
                EXPECT_EQ(nh.key().value(), i);
                EXPECT_EQ(nh.mapped().value(), i);
                // Insert with node
                m.insert(std::move(nh));
                EXPECT_EQ(m.size(), kSize);

                // Extract with iterator
                auto it = m.find(CopyableMovableInstance(i));
                nh = m.extract(it);
                EXPECT_EQ(m.size(), kSize - 1);
                EXPECT_EQ(nh.key().value(), i);
                EXPECT_EQ(nh.mapped().value(), i);
                // Insert with node and hint
                m.insert(m.begin(), std::move(nh));
                EXPECT_EQ(m.size(), kSize);
            }
        }
        EXPECT_EQ(0, tracker.instances());
    }

    TEST(Btree, ExtractTracking) {
        TestExtractWithTrackingForSet<phmap::btree_set<MovableOnlyInstance>>();
        TestExtractWithTrackingForSet<phmap::btree_multiset<MovableOnlyInstance>>();
        TestExtractWithTrackingForMap<
            phmap::btree_map<CopyableMovableInstance, MovableOnlyInstance>>();
        TestExtractWithTrackingForMap<
            phmap::btree_multimap<CopyableMovableInstance, MovableOnlyInstance>>();
    }

    TEST(Btree, ExtractAndInsertNodeHandleMultiSet) {
        phmap::btree_multiset<int> src1 = {1, 2, 3, 3, 4, 5};
        auto nh = src1.extract(src1.find(3));
        EXPECT_THAT(src1, ElementsAre(1, 2, 3, 4, 5));
        phmap::btree_multiset<int> other;
        auto res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(3));
        EXPECT_EQ(res, other.find(3));

        phmap::btree_multiset<int> src2 = {3, 4};
        nh = src2.extract(src2.find(3));
        EXPECT_THAT(src2, ElementsAre(4));
        res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(3, 3));
        EXPECT_EQ(res, ++other.find(3));
    }

    TEST(Btree, ExtractAndInsertNodeHandleMap) {
        phmap::btree_map<int, int> src1 = {{1, 2}, {3, 4}, {5, 6}};
        auto nh = src1.extract(src1.find(3));
        EXPECT_THAT(src1, ElementsAre(Pair(1, 2), Pair(5, 6)));
        phmap::btree_map<int, int> other;
        phmap::btree_map<int, int>::insert_return_type res =
            other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
        EXPECT_EQ(res.position, other.find(3));
        EXPECT_TRUE(res.inserted);
        EXPECT_TRUE(res.node.empty());

        phmap::btree_map<int, int> src2 = {{3, 6}};
        nh = src2.extract(src2.find(3));
        EXPECT_TRUE(src2.empty());
        res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
        EXPECT_EQ(res.position, other.find(3));
        EXPECT_FALSE(res.inserted);
        ASSERT_FALSE(res.node.empty());
        EXPECT_EQ(res.node.key(), 3);
        EXPECT_EQ(res.node.mapped(), 6);
    }

    TEST(Btree, ExtractAndInsertNodeHandleMultiMap) {
        phmap::btree_multimap<int, int> src1 = {{1, 2}, {3, 4}, {5, 6}};
        auto nh = src1.extract(src1.find(3));
        EXPECT_THAT(src1, ElementsAre(Pair(1, 2), Pair(5, 6)));
        phmap::btree_multimap<int, int> other;
        auto res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
        EXPECT_EQ(res, other.find(3));

        phmap::btree_multimap<int, int> src2 = {{3, 6}};
        nh = src2.extract(src2.find(3));
        EXPECT_TRUE(src2.empty());
        res = other.insert(std::move(nh));
        EXPECT_THAT(other, ElementsAre(Pair(3, 4), Pair(3, 6)));
        EXPECT_EQ(res, ++other.begin());
    }

    // For multisets, insert with hint also affects correctness because we need to
    // insert immediately before the hint if possible.
    struct InsertMultiHintData {
        int key;
        int not_key;
        bool operator==(const InsertMultiHintData other) const {
            return key == other.key && not_key == other.not_key;
        }
    };

    struct InsertMultiHintDataKeyCompare {
        using is_transparent = void;
        bool operator()(const InsertMultiHintData a,
                        const InsertMultiHintData b) const {
            return a.key < b.key;
        }
        bool operator()(const int a, const InsertMultiHintData b) const {
            return a < b.key;
        }
        bool operator()(const InsertMultiHintData a, const int b) const {
            return a.key < b;
        }
    };

    TEST(Btree, InsertHintNodeHandle) {
        // For unique sets, insert with hint is just a performance optimization.
        // Test that insert works correctly when the hint is right or wrong.
        {
            phmap::btree_set<int> src = {1, 2, 3, 4, 5};
            auto nh = src.extract(src.find(3));
            EXPECT_THAT(src, ElementsAre(1, 2, 4, 5));
            phmap::btree_set<int> other = {0, 100};
            // Test a correct hint.
            auto it = other.insert(other.lower_bound(3), std::move(nh));
            EXPECT_THAT(other, ElementsAre(0, 3, 100));
            EXPECT_EQ(it, other.find(3));

            nh = src.extract(src.find(5));
            // Test an incorrect hint.
            it = other.insert(other.end(), std::move(nh));
            EXPECT_THAT(other, ElementsAre(0, 3, 5, 100));
            EXPECT_EQ(it, other.find(5));
        }

        phmap::btree_multiset<InsertMultiHintData, InsertMultiHintDataKeyCompare> src =
            {{1, 2}, {3, 4}, {3, 5}};
        auto nh = src.extract(src.lower_bound(3));
        EXPECT_EQ(nh.value(), (InsertMultiHintData{3, 4}));
        phmap::btree_multiset<InsertMultiHintData, InsertMultiHintDataKeyCompare>
            other = {{3, 1}, {3, 2}, {3, 3}};
        auto it = other.insert(--other.end(), std::move(nh));
        EXPECT_THAT(
            other, ElementsAre(InsertMultiHintData{3, 1}, InsertMultiHintData{3, 2},
                               InsertMultiHintData{3, 4}, InsertMultiHintData{3, 3}));
        EXPECT_EQ(it, --(--other.end()));

        nh = src.extract(src.find(3));
        EXPECT_EQ(nh.value(), (InsertMultiHintData{3, 5}));
        it = other.insert(other.begin(), std::move(nh));
        EXPECT_THAT(other,
                    ElementsAre(InsertMultiHintData{3, 5}, InsertMultiHintData{3, 1},
                                InsertMultiHintData{3, 2}, InsertMultiHintData{3, 4},
                                InsertMultiHintData{3, 3}));
        EXPECT_EQ(it, other.begin());
    }

    struct IntCompareToCmp {
        phmap::weak_ordering operator()(int a, int b) const {
            if (a < b) return phmap::weak_ordering::less;
            if (a > b) return phmap::weak_ordering::greater;
            return phmap::weak_ordering::equivalent;
        }
    };

    TEST(Btree, MergeIntoUniqueContainers) {
        phmap::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
        phmap::btree_multiset<int> src2 = {3, 4, 4, 5};
        phmap::btree_set<int> dst;

        dst.merge(src1);
        EXPECT_TRUE(src1.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3));
        dst.merge(src2);
        EXPECT_THAT(src2, ElementsAre(3, 4));
        EXPECT_THAT(dst, ElementsAre(1, 2, 3, 4, 5));
    }

    TEST(Btree, MergeIntoUniqueContainersWithCompareTo) {
        phmap::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
        phmap::btree_multiset<int> src2 = {3, 4, 4, 5};
        phmap::btree_set<int, IntCompareToCmp> dst;

        dst.merge(src1);
        EXPECT_TRUE(src1.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3));
        dst.merge(src2);
        EXPECT_THAT(src2, ElementsAre(3, 4));
        EXPECT_THAT(dst, ElementsAre(1, 2, 3, 4, 5));
    }

    TEST(Btree, MergeIntoMultiContainers) {
        phmap::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
        phmap::btree_multiset<int> src2 = {3, 4, 4, 5};
        phmap::btree_multiset<int> dst;

        dst.merge(src1);
        EXPECT_TRUE(src1.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3));
        dst.merge(src2);
        EXPECT_TRUE(src2.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3, 3, 4, 4, 5));
    }

    TEST(Btree, MergeIntoMultiContainersWithCompareTo) {
        phmap::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
        phmap::btree_multiset<int> src2 = {3, 4, 4, 5};
        phmap::btree_multiset<int, IntCompareToCmp> dst;

        dst.merge(src1);
        EXPECT_TRUE(src1.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3));
        dst.merge(src2);
        EXPECT_TRUE(src2.empty());
        EXPECT_THAT(dst, ElementsAre(1, 2, 3, 3, 4, 4, 5));
    }

    TEST(Btree, MergeIntoMultiMapsWithDifferentComparators) {
        phmap::btree_map<int, int, IntCompareToCmp> src1 = {{1, 1}, {2, 2}, {3, 3}};
        phmap::btree_multimap<int, int, std::greater<int>> src2 = {
            {5, 5}, {4, 1}, {4, 4}, {3, 2}};
        phmap::btree_multimap<int, int> dst;

        dst.merge(src1);
        EXPECT_TRUE(src1.empty());
        EXPECT_THAT(dst, ElementsAre(Pair(1, 1), Pair(2, 2), Pair(3, 3)));
        dst.merge(src2);
        EXPECT_TRUE(src2.empty());
        EXPECT_THAT(dst, ElementsAre(Pair(1, 1), Pair(2, 2), Pair(3, 3), Pair(3, 2),
                                     Pair(4, 1), Pair(4, 4), Pair(5, 5)));
    }

    struct KeyCompareToWeakOrdering {
        template <typename T>
        phmap::weak_ordering operator()(const T &a, const T &b) const {
            return a < b ? phmap::weak_ordering::less
                       : a == b ? phmap::weak_ordering::equivalent
                       : phmap::weak_ordering::greater;
        }
    };

    struct KeyCompareToStrongOrdering {
        template <typename T>
        phmap::strong_ordering operator()(const T &a, const T &b) const {
            return a < b ? phmap::strong_ordering::less
                       : a == b ? phmap::strong_ordering::equal
                       : phmap::strong_ordering::greater;
        }
    };

    TEST(Btree, UserProvidedKeyCompareToComparators) {
        phmap::btree_set<int, KeyCompareToWeakOrdering> weak_set = {1, 2, 3};
        EXPECT_TRUE(weak_set.contains(2));
        EXPECT_FALSE(weak_set.contains(4));

        phmap::btree_set<int, KeyCompareToStrongOrdering> strong_set = {1, 2, 3};
        EXPECT_TRUE(strong_set.contains(2));
        EXPECT_FALSE(strong_set.contains(4));
    }

    TEST(Btree, TryEmplaceBasicTest) {
        phmap::btree_map<int, std::string> m;

        // Should construct a std::string from the literal.
        m.try_emplace(1, "one");
        EXPECT_EQ(1, m.size());

        // Try other std::string constructors and const lvalue key.
        const int key(42);
        m.try_emplace(key, 3, 'a');
        m.try_emplace(2, std::string("two"));

        EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
        EXPECT_THAT(m, ElementsAreArray(std::vector<std::pair<int, std::string>>{
                    {1, "one"}, {2, "two"}, {42, "aaa"}}));
    }

    TEST(Btree, TryEmplaceWithHintWorks) {
        // Use a counting comparator here to verify that hint is used.
        int calls = 0;
        auto cmp = [&calls](int x, int y) {
            ++calls;
            return x < y;
        };
        using Cmp = decltype(cmp);

        phmap::btree_map<int, int, Cmp> m(cmp);
        for (int i = 0; i < 128; ++i) {
            m.emplace(i, i);
        }

        // Sanity check for the comparator
        calls = 0;
        m.emplace(127, 127);
        EXPECT_GE(calls, 4);

        // Try with begin hint:
        calls = 0;
        auto it = m.try_emplace(m.begin(), -1, -1);
        EXPECT_EQ(129, m.size());
        EXPECT_EQ(it, m.begin());
        EXPECT_LE(calls, 2);

        // Try with end hint:
        calls = 0;
        std::pair<int, int> pair1024 = {1024, 1024};
        it = m.try_emplace(m.end(), pair1024.first, pair1024.second);
        EXPECT_EQ(130, m.size());
        EXPECT_EQ(it, --m.end());
        EXPECT_LE(calls, 2);

        // Try value already present, bad hint; ensure no duplicate added:
        calls = 0;
        it = m.try_emplace(m.end(), 16, 17);
        EXPECT_EQ(130, m.size());
        EXPECT_GE(calls, 4);
        EXPECT_EQ(it, m.find(16));

        // Try value already present, hint points directly to it:
        calls = 0;
        it = m.try_emplace(it, 16, 17);
        EXPECT_EQ(130, m.size());
        EXPECT_LE(calls, 2);
        EXPECT_EQ(it, m.find(16));

        m.erase(2);
        EXPECT_EQ(129, m.size());
        auto hint = m.find(3);
        // Try emplace in the middle of two other elements.
        calls = 0;
        m.try_emplace(hint, 2, 2);
        EXPECT_EQ(130, m.size());
        EXPECT_LE(calls, 2);

        EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
    }

    TEST(Btree, TryEmplaceWithBadHint) {
        phmap::btree_map<int, int> m = {{1, 1}, {9, 9}};

        // Bad hint (too small), should still emplace:
        auto it = m.try_emplace(m.begin(), 2, 2);
        EXPECT_EQ(it, ++m.begin());
        EXPECT_THAT(m, ElementsAreArray(
                        std::vector<std::pair<int, int>>{{1, 1}, {2, 2}, {9, 9}}));

        // Bad hint, too large this time:
        it = m.try_emplace(++(++m.begin()), 0, 0);
        EXPECT_EQ(it, m.begin());
        EXPECT_THAT(m, ElementsAreArray(std::vector<std::pair<int, int>>{
                    {0, 0}, {1, 1}, {2, 2}, {9, 9}}));
    }

    TEST(Btree, TryEmplaceMaintainsSortedOrder) {
        phmap::btree_map<int, std::string> m;
        std::pair<int, std::string> pair5 = {5, "five"};

        // Test both lvalue & rvalue emplace.
        m.try_emplace(10, "ten");
        m.try_emplace(pair5.first, pair5.second);
        EXPECT_EQ(2, m.size());
        EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));

        int int100{100};
        m.try_emplace(int100, "hundred");
        m.try_emplace(1, "one");
        EXPECT_EQ(4, m.size());
        EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
    }

    TEST(Btree, TryEmplaceWithHintAndNoValueArgsWorks) {
        phmap::btree_map<int, int> m;
        m.try_emplace(m.end(), 1);
        EXPECT_EQ(0, m[1]);
    }

    TEST(Btree, TryEmplaceWithHintAndMultipleValueArgsWorks) {
        phmap::btree_map<int, std::string> m;
        m.try_emplace(m.end(), 1, 10, 'a');
        EXPECT_EQ(std::string(10, 'a'), m[1]);
    }

    TEST(Btree, MoveAssignmentAllocatorPropagation) {
        InstanceTracker tracker;

        int64_t bytes1 = 0, bytes2 = 0;
        PropagatingCountingAlloc<MovableOnlyInstance> allocator1(&bytes1);
        PropagatingCountingAlloc<MovableOnlyInstance> allocator2(&bytes2);
        std::less<MovableOnlyInstance> cmp;

        // Test propagating allocator_type.
        {
            phmap::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
                             PropagatingCountingAlloc<MovableOnlyInstance>>
                set1(cmp, allocator1), set2(cmp, allocator2);

            for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));

            tracker.ResetCopiesMovesSwaps();
            set2 = std::move(set1);
            EXPECT_EQ(tracker.moves(), 0);
        }
        // Test non-propagating allocator_type with equal allocators.
        {
            phmap::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
                             CountingAllocator<MovableOnlyInstance>>
                set1(cmp, allocator1), set2(cmp, allocator1);

            for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));

            tracker.ResetCopiesMovesSwaps();
            set2 = std::move(set1);
            EXPECT_EQ(tracker.moves(), 0);
        }
        // Test non-propagating allocator_type with different allocators.
        {
            phmap::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
                             CountingAllocator<MovableOnlyInstance>>
                set1(cmp, allocator1), set2(cmp, allocator2);

            for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));

            tracker.ResetCopiesMovesSwaps();
            set2 = std::move(set1);
            EXPECT_GE(tracker.moves(), 100);
        }
    }

    TEST(Btree, EmptyTree) {
        phmap::btree_set<int> s;
        EXPECT_TRUE(s.empty());
        EXPECT_EQ(s.size(), 0);
        EXPECT_GT(s.max_size(), 0);
    }

    bool IsEven(int k) { return k % 2 == 0; }

    TEST(Btree, EraseIf) {
        // Test that erase_if works with all the container types and supports lambdas.
        {
            phmap::btree_set<int> s = {1, 3, 5, 6, 100};
            erase_if(s, [](int k) { return k > 3; });
            EXPECT_THAT(s, ElementsAre(1, 3));
        }
        {
            phmap::btree_multiset<int> s = {1, 3, 3, 5, 6, 6, 100};
            erase_if(s, [](int k) { return k <= 3; });
            EXPECT_THAT(s, ElementsAre(5, 6, 6, 100));
        }
        {
            phmap::btree_map<int, int> m = {{1, 1}, {3, 3}, {6, 6}, {100, 100}};
            erase_if(m, [](std::pair<const int, int> kv) { return kv.first > 3; });
            EXPECT_THAT(m, ElementsAre(Pair(1, 1), Pair(3, 3)));
        }
        {
            phmap::btree_multimap<int, int> m = {{1, 1}, {3, 3}, {3, 6},
                                                 {6, 6}, {6, 7}, {100, 6}};
            erase_if(m, [](std::pair<const int, int> kv) { return kv.second == 6; });
            EXPECT_THAT(m, ElementsAre(Pair(1, 1), Pair(3, 3), Pair(6, 7)));
        }
        // Test that erasing all elements from a large set works and test support for
        // function pointers.
        {
            phmap::btree_set<int> s;
            for (int i = 0; i < 1000; ++i) s.insert(2 * i);
            erase_if(s, IsEven);
            EXPECT_THAT(s, IsEmpty());
        }
        // Test that erase_if supports other format of function pointers.
        {
            phmap::btree_set<int> s = {1, 3, 5, 6, 100};
            erase_if(s, &IsEven);
            EXPECT_THAT(s, ElementsAre(1, 3, 5));
        }
    }

}  // namespace
}  // namespace priv
}  // namespace phmap