diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.binary.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.binary.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.binary.pass.cpp
@@ -0,0 +1,426 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <algorithm>
+
+// template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+//          weakly_incrementable O, copy_constructible F, class Proj1 = identity,
+//          class Proj2 = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<I1, Proj1>,
+//                                          projected<I2, Proj2>>>
+//   constexpr ranges::binary_transform_result<I1, I2, O>
+//     ranges::transform(I1 first1, S1 last1, I2 first2, S2 last2, O result,
+//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
+// template<input_range R1, input_range R2, weakly_incrementable O,
+//          copy_constructible F, class Proj1 = identity, class Proj2 = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
+//                                          projected<iterator_t<R2>, Proj2>>>
+//   constexpr ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
+//     ranges::transform(R1&& r1, R2&& r2, O result,
+//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <functional>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "almost_satisfies_types.h"
+
+struct BinaryFunc {
+  int operator()(int, int);
+};
+
+template <class Range>
+concept HasTranformR = requires(Range r, int* out) { std::ranges::transform(r, r, out, BinaryFunc{}); };
+
+static_assert(HasTranformR<std::array<int, 1>>);
+static_assert(!HasTranformR<int>);
+static_assert(!HasTranformR<InputRangeNotDerivedFrom>);
+static_assert(!HasTranformR<InputRangeNotIndirectlyReadable>);
+static_assert(!HasTranformR<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasTranformR<InputRangeNotSentinelSemiregular>);
+static_assert(!HasTranformR<InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It, class Sent = It>
+concept HasTransformIt =
+    requires(It it, Sent sent, int* out) { std::ranges::transform(it, sent, it, sent, out, BinaryFunc{}); };
+static_assert(HasTransformIt<int*>);
+static_assert(!HasTransformIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasTransformIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasTransformIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It>
+concept HasTransformOut = requires(int* it, int* sent, It out, std::array<int, 2> range) {
+  std::ranges::transform(it, sent, it, sent, out, BinaryFunc{});
+  std::ranges::transform(range, range, out, BinaryFunc{});
+};
+static_assert(HasTransformOut<int*>);
+static_assert(!HasTransformOut<WeaklyIncrementableNotMovable>);
+
+// check indirectly_readable
+static_assert(HasTransformOut<char*>);
+static_assert(!HasTransformOut<int**>);
+
+struct MoveOnlyFunctor {
+  MoveOnlyFunctor(const MoveOnlyFunctor&) = delete;
+  MoveOnlyFunctor(MoveOnlyFunctor&&)      = default;
+  int operator()(int, int);
+};
+
+template <class Func>
+concept HasTransformFuncBinary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
+  std::ranges::transform(it, sent, it, sent, out, func);
+  std::ranges::transform(range, range, out, func);
+};
+static_assert(HasTransformFuncBinary<BinaryFunc>);
+static_assert(!HasTransformFuncBinary<MoveOnlyFunctor>);
+
+static_assert(std::is_same_v<std::ranges::binary_transform_result<int, long, char>,
+                             std::ranges::in_in_out_result<int, long, char>>);
+
+// clang-format off
+template <class In1, class In2, class Out, class Sent1, class Sent2>
+constexpr bool test_iterators() {
+  { // simple
+    {
+      int a[] = {1, 2, 3, 4, 5};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+      assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
+      assert(base(ret.in1) == a + 5);
+      assert(base(ret.in2) == b + 5);
+      assert(base(ret.out) == c + 5);
+    }
+
+    {
+      int a[] = {1, 2, 3, 4, 5};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+      std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
+          range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
+      assert(base(ret.in1) == a + 5);
+      assert(base(ret.in2) == b + 5);
+      assert(base(ret.out) == c + 5);
+    }
+  }
+
+  { // first range empty
+    {
+      int a[] = {};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+
+    {
+      int a[] = {};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+  }
+
+  { // second range empty
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+  }
+
+  { // both ranges empty
+    {
+      int a[] = {};
+      int b[] = {};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+
+    {
+      int a[] = {};
+      int b[] = {};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(base(ret.in1) == a);
+      assert(base(ret.in2) == b);
+      assert(base(ret.out) == c);
+    }
+  }
+
+  { // first range one element
+    {
+      int a[] = {2};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 1)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 7);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+
+    {
+      int a[] = {2};
+      int b[] = {5, 4, 3, 2, 1};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 7);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+  }
+
+  { // second range contains one element
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {4};
+      int c[5];
+
+      auto ret = std::ranges::transform(
+          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 1)), Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 9);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+
+    {
+      int a[] = {5, 4, 3, 2, 1};
+      int b[] = {4};
+      int c[5];
+
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 1)));
+
+      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
+
+      assert(c[0] == 9);
+      assert(base(ret.in1) == a + 1);
+      assert(base(ret.in2) == b + 1);
+      assert(base(ret.out) == c + 1);
+    }
+  }
+
+  { // check that the transform function and projection call counts are correct
+    {
+      int predCount = 0;
+      int proj1Count = 0;
+      int proj2Count = 0;
+      auto pred = [&](int, int) { ++predCount; return 1; };
+      auto proj1 = [&](int) { ++proj1Count; return 0; };
+      auto proj2 = [&](int) { ++proj2Count; return 0; };
+      int a[] = {1, 2, 3, 4};
+      int b[] = {1, 2, 3, 4};
+      std::array<int, 4> c;
+      std::ranges::transform(In1(a), Sent1(In1(a + 4)), In2(b), Sent2(In2(b + 4)), Out(c.data()), pred, proj1, proj2);
+      assert(predCount == 4);
+      assert(proj1Count == 4);
+      assert(proj2Count == 4);
+      assert((c == std::array{1, 1, 1, 1}));
+    }
+    {
+      int predCount = 0;
+      int proj1Count = 0;
+      int proj2Count = 0;
+      auto pred = [&](int, int) { ++predCount; return 1; };
+      auto proj1 = [&](int) { ++proj1Count; return 0; };
+      auto proj2 = [&](int) { ++proj2Count; return 0; };
+      int a[] = {1, 2, 3, 4};
+      int b[] = {1, 2, 3, 4};
+      std::array<int, 4> c;
+      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
+      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 4)));
+      std::ranges::transform(range1, range2, Out(c.data()), pred, proj1, proj2);
+      assert(predCount == 4);
+      assert(proj1Count == 4);
+      assert(proj2Count == 4);
+      assert((c == std::array{1, 1, 1, 1}));
+    }
+  }
+
+  return true;
+}
+// clang-format on
+
+template <class In2, class Out, class Sent2 = In2>
+constexpr void test_iterator_in1() {
+  test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>();
+  test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>();
+  test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>();
+  test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>();
+  test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>();
+  test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>();
+  test_iterators<int*, In2, Out, int*, Sent2>();
+  // static_asserting here to avoid hitting the constant evaluation step limit
+  static_assert(test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>());
+  static_assert(test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>());
+  static_assert(test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>());
+  static_assert(test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>());
+  static_assert(test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>());
+  static_assert(test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>());
+  static_assert(test_iterators<int*, In2, Out, int*, Sent2>());
+}
+
+template <class Out>
+void test_iterators_in1_in2() {
+  test_iterator_in1<cpp17_input_iterator<int*>, Out, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  test_iterator_in1<cpp20_input_iterator<int*>, Out, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  test_iterator_in1<forward_iterator<int*>, Out>();
+  test_iterator_in1<bidirectional_iterator<int*>, Out>();
+  test_iterator_in1<random_access_iterator<int*>, Out>();
+  test_iterator_in1<contiguous_iterator<int*>, Out>();
+  test_iterator_in1<int*, Out>();
+}
+
+constexpr bool test() {
+  { // check that std::ranges::dangling is returned properly
+    {
+      int b[] = {2, 5, 4, 3, 1};
+      std::array<int, 5> c;
+      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, int*, int*>> auto ret =
+          std::ranges::transform(std::array{1, 2, 3, 5, 4}, b, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{2, 10, 12, 15, 4}));
+      assert(ret.in2 == b + 5);
+      assert(ret.out == c.data() + c.size());
+    }
+    {
+      int a[] = {2, 5, 4, 3, 1, 4, 5, 6};
+      std::array<int, 8> c;
+      std::same_as<std::ranges::in_in_out_result<int*, std::ranges::dangling, int*>> auto ret =
+          std::ranges::transform(a, std::array{1, 2, 3, 5, 4, 5, 6, 7}, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{2, 10, 12, 15, 4, 20, 30, 42}));
+      assert(ret.in1 == a + 8);
+      assert(ret.out == c.data() + c.size());
+    }
+    {
+      std::array<int, 3> c;
+      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, std::ranges::dangling, int*>> auto ret =
+          std::ranges::transform(std::array{4, 4, 4}, std::array{4, 4, 4}, c.data(), [](int i, int j) { return i * j; });
+      assert((c == std::array{16, 16, 16}));
+      assert(ret.out == c.data() + c.size());
+    }
+  }
+
+  { // check that returning another type from the projection works
+    {
+      struct S { int i; int other; };
+      S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+      S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
+      std::array<int, 4> c;
+      std::ranges::transform(a, a + 4, b, b + 4, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
+      assert((c == std::array{10, 21, 33, 50}));
+    }
+    {
+      struct S { int i; int other; };
+      S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+      S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
+      std::array<int, 4> c;
+      std::ranges::transform(a, b, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
+      assert((c == std::array{10, 21, 33, 50}));
+    }
+  }
+
+  { // check that std::invoke is used
+    struct S { int i; };
+    S a[] = { S{1}, S{3}, S{2} };
+    S b[] = { S{2}, S{5}, S{3} };
+    std::array<int, 3> c;
+    auto ret = std::ranges::transform(a, b, c.data(), [](int i, int j) { return i + j + 2; }, &S::i, &S::i);
+    assert((c == std::array{5, 10, 7}));
+    assert(ret.out == c.data() + 3);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test_iterators_in1_in2<cpp17_output_iterator<int*>>();
+  test_iterators_in1_in2<cpp20_output_iterator<int*>>();
+  test_iterators_in1_in2<forward_iterator<int*>>();
+  test_iterators_in1_in2<bidirectional_iterator<int*>>();
+  test_iterators_in1_in2<random_access_iterator<int*>>();
+  test_iterators_in1_in2<contiguous_iterator<int*>>();
+  test_iterators_in1_in2<int*>();
+  test();
+  static_assert(test());
+
+  return 0;
+}
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp
deleted file mode 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp
+++ /dev/null
@@ -1,584 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-
-// <algorithm>
-
-// template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
-//          copy_constructible F, class Proj = identity>
-//   requires indirectly_writable<O, indirect_result_t<F&, projected<I, Proj>>>
-//   constexpr ranges::unary_transform_result<I, O>
-//     ranges::transform(I first1, S last1, O result, F op, Proj proj = {});
-// template<input_range R, weakly_incrementable O, copy_constructible F,
-//          class Proj = identity>
-//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
-//   constexpr ranges::unary_transform_result<borrowed_iterator_t<R>, O>
-//     ranges::transform(R&& r, O result, F op, Proj proj = {});
-// template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
-//          weakly_incrementable O, copy_constructible F, class Proj1 = identity,
-//          class Proj2 = identity>
-//   requires indirectly_writable<O, indirect_result_t<F&, projected<I1, Proj1>,
-//                                          projected<I2, Proj2>>>
-//   constexpr ranges::binary_transform_result<I1, I2, O>
-//     ranges::transform(I1 first1, S1 last1, I2 first2, S2 last2, O result,
-//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
-// template<input_range R1, input_range R2, weakly_incrementable O,
-//          copy_constructible F, class Proj1 = identity, class Proj2 = identity>
-//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
-//                                          projected<iterator_t<R2>, Proj2>>>
-//   constexpr ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
-//     ranges::transform(R1&& r1, R2&& r2, O result,
-//                       F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
-
-#include <algorithm>
-#include <array>
-#include <cassert>
-#include <functional>
-#include <ranges>
-
-#include "test_iterators.h"
-#include "almost_satisfies_types.h"
-
-struct BinaryFunc {
-  int operator()(int, int);
-};
-
-template <class Range>
-concept HasTranformR = requires(Range r, int* out) {
-  std::ranges::transform(r, out, std::identity{});
-  std::ranges::transform(r, r, out, BinaryFunc{});
-};
-static_assert(HasTranformR<std::array<int, 1>>);
-static_assert(!HasTranformR<int>);
-static_assert(!HasTranformR<InputRangeNotDerivedFrom>);
-static_assert(!HasTranformR<InputRangeNotIndirectlyReadable>);
-static_assert(!HasTranformR<InputRangeNotInputOrOutputIterator>);
-static_assert(!HasTranformR<InputRangeNotSentinelSemiregular>);
-static_assert(!HasTranformR<InputRangeNotSentinelEqualityComparableWith>);
-
-template <class It, class Sent = It>
-concept HasTransformIt = requires(It it, Sent sent, int* out) {
-  std::ranges::transform(it, sent, out, std::identity{});
-  std::ranges::transform(it, sent, it, sent, out, BinaryFunc{});
-};
-static_assert(HasTransformIt<int*>);
-static_assert(!HasTransformIt<InputIteratorNotDerivedFrom>);
-static_assert(!HasTransformIt<InputIteratorNotIndirectlyReadable>);
-static_assert(!HasTransformIt<InputIteratorNotInputOrOutputIterator>);
-static_assert(!HasTransformIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
-static_assert(!HasTransformIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
-
-template <class It>
-concept HasTransformOut = requires(int* it, int* sent, It out, std::array<int, 2> range) {
-  std::ranges::transform(it, sent, out, std::identity{});
-  std::ranges::transform(it, sent, it, sent, out, BinaryFunc{});
-  std::ranges::transform(range, out, std::identity{});
-  std::ranges::transform(range, range, out, BinaryFunc{});
-};
-static_assert(HasTransformOut<int*>);
-static_assert(!HasTransformOut<WeaklyIncrementableNotMovable>);
-
-// check indirectly_readable
-static_assert(HasTransformOut<char*>);
-static_assert(!HasTransformOut<int**>);
-
-struct MoveOnlyFunctor {
-  MoveOnlyFunctor(const MoveOnlyFunctor&) = delete;
-  MoveOnlyFunctor(MoveOnlyFunctor&&) = default;
-  int operator()(int);
-  int operator()(int, int);
-};
-
-template <class Func>
-concept HasTransformFuncUnary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
-  std::ranges::transform(it, sent, out, func);
-  std::ranges::transform(range, out, func);
-};
-static_assert(HasTransformFuncUnary<std::identity>);
-static_assert(!HasTransformFuncUnary<MoveOnlyFunctor>);
-
-template <class Func>
-concept HasTransformFuncBinary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
-  std::ranges::transform(it, sent, it, sent, out, func);
-  std::ranges::transform(range, range, out, func);
-};
-static_assert(HasTransformFuncBinary<BinaryFunc>);
-static_assert(!HasTransformFuncBinary<MoveOnlyFunctor>);
-
-static_assert(std::is_same_v<std::ranges::unary_transform_result<int, long>, std::ranges::in_out_result<int, long>>);
-static_assert(std::is_same_v<std::ranges::binary_transform_result<int, long, char>,
-                             std::ranges::in_in_out_result<int, long, char>>);
-
-template <class In1, class In2, class Out, class Sent1, class Sent2>
-constexpr bool test_iterators() {
-  { // simple
-    { // unary
-      {
-        int a[] = {1, 2, 3, 4, 5};
-        int b[5];
-        std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
-          std::ranges::transform(In1(a), Sent1(In1(a + 5)), Out(b), [](int i) { return i * 2; });
-        assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
-        assert(base(ret.in) == a + 5);
-        assert(base(ret.out) == b + 5);
-      }
-
-      {
-        int a[] = {1, 2, 3, 4, 5};
-        int b[5];
-        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
-        std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
-          std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
-        assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
-        assert(base(ret.in) == a + 5);
-        assert(base(ret.out) == b + 5);
-      }
-    }
-
-    { // binary
-      {
-        int a[] = {1, 2, 3, 4, 5};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
-            In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
-
-        assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
-        assert(base(ret.in1) == a + 5);
-        assert(base(ret.in2) == b + 5);
-        assert(base(ret.out) == c + 5);
-      }
-
-      {
-        int a[] = {1, 2, 3, 4, 5};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
-        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
-
-        std::same_as<std::ranges::in_in_out_result<In1, In2, Out>> decltype(auto) ret = std::ranges::transform(
-            range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-        assert((std::to_array(c) == std::array{6, 6, 6, 6, 6}));
-        assert(base(ret.in1) == a + 5);
-        assert(base(ret.in2) == b + 5);
-        assert(base(ret.out) == c + 5);
-      }
-    }
-  }
-
-  { // first range empty
-    { // unary
-      {
-        int a[] = {};
-        int b[5];
-        auto ret = std::ranges::transform(In1(a), Sent1(In1(a)), Out(b), [](int i) { return i * 2; });
-        assert(base(ret.in) == a);
-        assert(base(ret.out) == b);
-      }
-
-      {
-        int a[] = {};
-        int b[5];
-        auto range = std::ranges::subrange(In1(a), Sent1(In1(a)));
-        auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
-        assert(base(ret.in) == a);
-        assert(base(ret.out) == b);
-      }
-    }
-
-    { // binary
-      {
-        int a[] = {};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        auto ret = std::ranges::transform(
-            In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
-
-        assert(base(ret.in1) == a);
-        assert(base(ret.in2) == b);
-        assert(base(ret.out) == c);
-      }
-
-      {
-        int a[] = {};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
-        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
-
-        auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-        assert(base(ret.in1) == a);
-        assert(base(ret.in2) == b);
-        assert(base(ret.out) == c);
-      }
-    }
-  }
-
-  { // second range empty (binary)
-    {
-      int a[] = {5, 4, 3, 2, 1};
-      int b[] = {};
-      int c[5];
-
-      auto ret = std::ranges::transform(
-          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
-
-      assert(base(ret.in1) == a);
-      assert(base(ret.in2) == b);
-      assert(base(ret.out) == c);
-    }
-
-    {
-      int a[] = {5, 4, 3, 2, 1};
-      int b[] = {};
-      int c[5];
-
-      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
-      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
-
-      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-      assert(base(ret.in1) == a);
-      assert(base(ret.in2) == b);
-      assert(base(ret.out) == c);
-    }
-  }
-
-  { // both ranges empty (binary)
-    {
-      int a[] = {};
-      int b[] = {};
-      int c[5];
-
-      auto ret = std::ranges::transform(
-          In1(a), Sent1(In1(a)), In2(b), Sent2(In2(b)), Out(c), [](int i, int j) { return i + j; });
-
-      assert(base(ret.in1) == a);
-      assert(base(ret.in2) == b);
-      assert(base(ret.out) == c);
-    }
-
-    {
-      int a[] = {};
-      int b[] = {};
-      int c[5];
-
-      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a)));
-      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b)));
-
-      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-      assert(base(ret.in1) == a);
-      assert(base(ret.in2) == b);
-      assert(base(ret.out) == c);
-    }
-  }
-
-  { // first range one element
-    { // unary
-      {
-        int a[] = {2};
-        int b[5];
-        auto ret = std::ranges::transform(In1(a), Sent1(In1(a + 1)), Out(b), [](int i) { return i * 2; });
-        assert(b[0] == 4);
-        assert(base(ret.in) == a + 1);
-        assert(base(ret.out) == b + 1);
-      }
-
-      {
-        int a[] = {2};
-        int b[5];
-        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
-        auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
-        assert(b[0] == 4);
-        assert(base(ret.in) == a + 1);
-        assert(base(ret.out) == b + 1);
-      }
-    }
-
-    { // binary
-      {
-        int a[] = {2};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        auto ret = std::ranges::transform(
-            In1(a), Sent1(In1(a + 1)), In2(b), Sent2(In2(b + 5)), Out(c), [](int i, int j) { return i + j; });
-
-        assert(c[0] == 7);
-        assert(base(ret.in1) == a + 1);
-        assert(base(ret.in2) == b + 1);
-        assert(base(ret.out) == c + 1);
-      }
-
-      {
-        int a[] = {2};
-        int b[] = {5, 4, 3, 2, 1};
-        int c[5];
-
-        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
-        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 5)));
-
-        auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-        assert(c[0] == 7);
-        assert(base(ret.in1) == a + 1);
-        assert(base(ret.in2) == b + 1);
-        assert(base(ret.out) == c + 1);
-      }
-    }
-  }
-
-  { // second range contains one element (binary)
-    {
-      int a[] = {5, 4, 3, 2, 1};
-      int b[] = {4};
-      int c[5];
-
-      auto ret = std::ranges::transform(
-          In1(a), Sent1(In1(a + 5)), In2(b), Sent2(In2(b + 1)), Out(c), [](int i, int j) { return i + j; });
-
-      assert(c[0] == 9);
-      assert(base(ret.in1) == a + 1);
-      assert(base(ret.in2) == b + 1);
-      assert(base(ret.out) == c + 1);
-    }
-
-    {
-      int a[] = {5, 4, 3, 2, 1};
-      int b[] = {4};
-      int c[5];
-
-      auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
-      auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 1)));
-
-      auto ret = std::ranges::transform(range1, range2, Out(c), [](int i, int j) { return i + j; });
-
-      assert(c[0] == 9);
-      assert(base(ret.in1) == a + 1);
-      assert(base(ret.in2) == b + 1);
-      assert(base(ret.out) == c + 1);
-    }
-  }
-
-  { // check that the transform function and projection call counts are correct
-    { // unary
-      {
-        int predCount = 0;
-        int projCount = 0;
-        auto pred = [&](int) { ++predCount; return 1; };
-        auto proj = [&](int) { ++projCount; return 0; };
-        int a[] = {1, 2, 3, 4};
-        std::array<int, 4> c;
-        std::ranges::transform(In1(a), Sent1(In1(a + 4)), Out(c.data()), pred, proj);
-        assert(predCount == 4);
-        assert(projCount == 4);
-        assert((c == std::array{1, 1, 1, 1}));
-      }
-      {
-        int predCount = 0;
-        int projCount = 0;
-        auto pred = [&](int) { ++predCount; return 1; };
-        auto proj = [&](int) { ++projCount; return 0; };
-        int a[] = {1, 2, 3, 4};
-        std::array<int, 4> c;
-        auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
-        std::ranges::transform(range, Out(c.data()), pred, proj);
-        assert(predCount == 4);
-        assert(projCount == 4);
-        assert((c == std::array{1, 1, 1, 1}));
-      }
-    }
-    { // binary
-      {
-        int predCount = 0;
-        int proj1Count = 0;
-        int proj2Count = 0;
-        auto pred = [&](int, int) { ++predCount; return 1; };
-        auto proj1 = [&](int) { ++proj1Count; return 0; };
-        auto proj2 = [&](int) { ++proj2Count; return 0; };
-        int a[] = {1, 2, 3, 4};
-        int b[] = {1, 2, 3, 4};
-        std::array<int, 4> c;
-        std::ranges::transform(In1(a), Sent1(In1(a + 4)), In2(b), Sent2(In2(b + 4)), Out(c.data()), pred, proj1, proj2);
-        assert(predCount == 4);
-        assert(proj1Count == 4);
-        assert(proj2Count == 4);
-        assert((c == std::array{1, 1, 1, 1}));
-      }
-      {
-        int predCount = 0;
-        int proj1Count = 0;
-        int proj2Count = 0;
-        auto pred = [&](int, int) { ++predCount; return 1; };
-        auto proj1 = [&](int) { ++proj1Count; return 0; };
-        auto proj2 = [&](int) { ++proj2Count; return 0; };
-        int a[] = {1, 2, 3, 4};
-        int b[] = {1, 2, 3, 4};
-        std::array<int, 4> c;
-        auto range1 = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
-        auto range2 = std::ranges::subrange(In2(b), Sent2(In2(b + 4)));
-        std::ranges::transform(range1, range2, Out(c.data()), pred, proj1, proj2);
-        assert(predCount == 4);
-        assert(proj1Count == 4);
-        assert(proj2Count == 4);
-        assert((c == std::array{1, 1, 1, 1}));
-      }
-    }
-  }
-
-  return true;
-}
-
-template <class In2, class Out, class Sent2 = In2>
-constexpr void test_iterator_in1() {
-  test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>();
-  test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>();
-  test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>();
-  test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>();
-  test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>();
-  test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>();
-  test_iterators<int*, In2, Out, int*, Sent2>();
-  // static_asserting here to avoid hitting the constant evaluation step limit
-  static_assert(test_iterators<cpp17_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp17_input_iterator<int*>>, Sent2>());
-  static_assert(test_iterators<cpp20_input_iterator<int*>, In2, Out, sentinel_wrapper<cpp20_input_iterator<int*>>, Sent2>());
-  static_assert(test_iterators<forward_iterator<int*>, In2, Out, forward_iterator<int*>, Sent2>());
-  static_assert(test_iterators<bidirectional_iterator<int*>, In2, Out, bidirectional_iterator<int*>, Sent2>());
-  static_assert(test_iterators<random_access_iterator<int*>, In2, Out, random_access_iterator<int*>, Sent2>());
-  static_assert(test_iterators<contiguous_iterator<int*>, In2, Out, contiguous_iterator<int*>, Sent2>());
-  static_assert(test_iterators<int*, In2, Out, int*, Sent2>());
-}
-
-template <class Out>
-void test_iterators_in1_in2() {
-  test_iterator_in1<cpp17_input_iterator<int*>, Out, sentinel_wrapper<cpp17_input_iterator<int*>>>();
-  test_iterator_in1<cpp20_input_iterator<int*>, Out, sentinel_wrapper<cpp20_input_iterator<int*>>>();
-  test_iterator_in1<forward_iterator<int*>, Out>();
-  test_iterator_in1<bidirectional_iterator<int*>, Out>();
-  test_iterator_in1<random_access_iterator<int*>, Out>();
-  test_iterator_in1<contiguous_iterator<int*>, Out>();
-  test_iterator_in1<int*, Out>();
-}
-
-constexpr bool test() {
-  { // check that std::ranges::dangling is returned properly
-    { // unary
-      std::array<int, 5> b;
-      std::same_as<std::ranges::in_out_result<std::ranges::dangling, int*>> auto ret =
-          std::ranges::transform(std::array{1, 2, 3, 5, 4}, b.data(), [](int i) { return i * i; });
-      assert((b == std::array{1, 4, 9, 25, 16}));
-      assert(ret.out == b.data() + b.size());
-    }
-    // binary
-    {
-      int b[] = {2, 5, 4, 3, 1};
-      std::array<int, 5> c;
-      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, int*, int*>> auto ret =
-          std::ranges::transform(std::array{1, 2, 3, 5, 4}, b, c.data(), [](int i, int j) { return i * j; });
-      assert((c == std::array{2, 10, 12, 15, 4}));
-      assert(ret.in2 == b + 5);
-      assert(ret.out == c.data() + c.size());
-    }
-    {
-      int a[] = {2, 5, 4, 3, 1, 4, 5, 6};
-      std::array<int, 8> c;
-      std::same_as<std::ranges::in_in_out_result<int*, std::ranges::dangling, int*>> auto ret =
-          std::ranges::transform(a, std::array{1, 2, 3, 5, 4, 5, 6, 7}, c.data(), [](int i, int j) { return i * j; });
-      assert((c == std::array{2, 10, 12, 15, 4, 20, 30, 42}));
-      assert(ret.in1 == a + 8);
-      assert(ret.out == c.data() + c.size());
-    }
-    {
-      std::array<int, 3> c;
-      std::same_as<std::ranges::in_in_out_result<std::ranges::dangling, std::ranges::dangling, int*>> auto ret =
-          std::ranges::transform(std::array{4, 4, 4}, std::array{4, 4, 4}, c.data(), [](int i, int j) { return i * j; });
-      assert((c == std::array{16, 16, 16}));
-      assert(ret.out == c.data() + c.size());
-    }
-  }
-
-  { // check that returning another type from the projection works
-    { // unary
-      {
-        struct S { int i; int other; };
-        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
-        std::array<int, 4> b;
-        std::ranges::transform(a, a + 4, b.begin(), [](S s) { return s.i; });
-        assert((b == std::array{0, 1, 3, 10}));
-      }
-      {
-        struct S { int i; int other; };
-        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
-        std::array<int, 4> b;
-        std::ranges::transform(a, b.begin(), [](S s) { return s.i; });
-        assert((b == std::array{0, 1, 3, 10}));
-      }
-    }
-    { // binary
-      {
-        struct S { int i; int other; };
-        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
-        S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
-        std::array<int, 4> c;
-        std::ranges::transform(a, a + 4, b, b + 4, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
-        assert((c == std::array{10, 21, 33, 50}));
-      }
-      {
-        struct S { int i; int other; };
-        S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
-        S b[] = { S{0, 10}, S{1, 20}, S{3, 30}, S{10, 40} };
-        std::array<int, 4> c;
-        std::ranges::transform(a, b, c.begin(), [](S s1, S s2) { return s1.i + s2.other; });
-        assert((c == std::array{10, 21, 33, 50}));
-      }
-    }
-  }
-
-  { // check that std::invoke is used
-    { // unary
-      struct S { int i; };
-      S a[] = { S{1}, S{3}, S{2} };
-      std::array<int, 3> b;
-      auto ret = std::ranges::transform(a, b.data(), [](int i) { return i; }, &S::i);
-      assert((b == std::array{1, 3, 2}));
-      assert(ret.out == b.data() + 3);
-    }
-    { // binary
-      struct S { int i; };
-      S a[] = { S{1}, S{3}, S{2} };
-      S b[] = { S{2}, S{5}, S{3} };
-      std::array<int, 3> c;
-      auto ret = std::ranges::transform(a, b, c.data(), [](int i, int j) { return i + j + 2; }, &S::i, &S::i);
-      assert((c == std::array{5, 10, 7}));
-      assert(ret.out == c.data() + 3);
-    }
-  }
-
-  return true;
-}
-
-int main(int, char**) {
-  test_iterators_in1_in2<cpp17_output_iterator<int*>>();
-  test_iterators_in1_in2<cpp20_output_iterator<int*>>();
-  test_iterators_in1_in2<forward_iterator<int*>>();
-  test_iterators_in1_in2<bidirectional_iterator<int*>>();
-  test_iterators_in1_in2<random_access_iterator<int*>>();
-  test_iterators_in1_in2<contiguous_iterator<int*>>();
-  test_iterators_in1_in2<int*>();
-  test();
-  static_assert(test());
-
-  return 0;
-}
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.unary.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.unary.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.unary.pass.cpp
@@ -0,0 +1,249 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <algorithm>
+
+// template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
+//          copy_constructible F, class Proj = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<I, Proj>>>
+//   constexpr ranges::unary_transform_result<I, O>
+//     ranges::transform(I first1, S last1, O result, F op, Proj proj = {});
+// template<input_range R, weakly_incrementable O, copy_constructible F,
+//          class Proj = identity>
+//   requires indirectly_writable<O, indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
+//   constexpr ranges::unary_transform_result<borrowed_iterator_t<R>, O>
+//     ranges::transform(R&& r, O result, F op, Proj proj = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <functional>
+#include <ranges>
+
+#include "test_iterators.h"
+#include "almost_satisfies_types.h"
+
+template <class Range>
+concept HasTranformR = requires(Range r, int* out) { std::ranges::transform(r, out, std::identity{}); };
+
+static_assert(HasTranformR<std::array<int, 1>>);
+static_assert(!HasTranformR<int>);
+static_assert(!HasTranformR<InputRangeNotDerivedFrom>);
+static_assert(!HasTranformR<InputRangeNotIndirectlyReadable>);
+static_assert(!HasTranformR<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasTranformR<InputRangeNotSentinelSemiregular>);
+static_assert(!HasTranformR<InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It, class Sent = It>
+concept HasTransformIt =
+    requires(It it, Sent sent, int* out) { std::ranges::transform(it, sent, out, std::identity{}); };
+
+static_assert(HasTransformIt<int*>);
+static_assert(!HasTransformIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasTransformIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasTransformIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasTransformIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+
+template <class It>
+concept HasTransformOut = requires(int* it, int* sent, It out, std::array<int, 2> range) {
+  std::ranges::transform(it, sent, out, std::identity{});
+  std::ranges::transform(range, out, std::identity{});
+};
+static_assert(HasTransformOut<int*>);
+static_assert(!HasTransformOut<WeaklyIncrementableNotMovable>);
+
+// check indirectly_readable
+static_assert(HasTransformOut<char*>);
+static_assert(!HasTransformOut<int**>);
+
+struct MoveOnlyFunctor {
+  MoveOnlyFunctor(const MoveOnlyFunctor&) = delete;
+  MoveOnlyFunctor(MoveOnlyFunctor&&)      = default;
+  int operator()(int);
+};
+
+template <class Func>
+concept HasTransformFuncUnary = requires(int* it, int* sent, int* out, std::array<int, 2> range, Func func) {
+  std::ranges::transform(it, sent, out, func);
+  std::ranges::transform(range, out, func);
+};
+static_assert(HasTransformFuncUnary<std::identity>);
+static_assert(!HasTransformFuncUnary<MoveOnlyFunctor>);
+
+static_assert(std::is_same_v<std::ranges::unary_transform_result<int, long>, std::ranges::in_out_result<int, long>>);
+
+// clang-format off
+template <class In1, class Out, class Sent1>
+constexpr bool test_iterators() {
+  { // simple
+    {
+      int a[] = {1, 2, 3, 4, 5};
+      int b[5];
+      std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
+        std::ranges::transform(In1(a), Sent1(In1(a + 5)), Out(b), [](int i) { return i * 2; });
+      assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
+      assert(base(ret.in) == a + 5);
+      assert(base(ret.out) == b + 5);
+    }
+
+    {
+      int a[] = {1, 2, 3, 4, 5};
+      int b[5];
+      auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 5)));
+      std::same_as<std::ranges::in_out_result<In1, Out>> decltype(auto) ret =
+        std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+      assert((std::to_array(b) == std::array{2, 4, 6, 8, 10}));
+      assert(base(ret.in) == a + 5);
+      assert(base(ret.out) == b + 5);
+    }
+  }
+
+  { // first range empty
+    {
+      int a[] = {};
+      int b[5];
+      auto ret = std::ranges::transform(In1(a), Sent1(In1(a)), Out(b), [](int i) { return i * 2; });
+      assert(base(ret.in) == a);
+      assert(base(ret.out) == b);
+    }
+
+    {
+      int a[] = {};
+      int b[5];
+      auto range = std::ranges::subrange(In1(a), Sent1(In1(a)));
+      auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+      assert(base(ret.in) == a);
+      assert(base(ret.out) == b);
+    }
+  }
+
+  { // one element range
+    {
+      int a[] = {2};
+      int b[5];
+      auto ret = std::ranges::transform(In1(a), Sent1(In1(a + 1)), Out(b), [](int i) { return i * 2; });
+      assert(b[0] == 4);
+      assert(base(ret.in) == a + 1);
+      assert(base(ret.out) == b + 1);
+    }
+
+    {
+      int a[] = {2};
+      int b[5];
+      auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 1)));
+      auto ret = std::ranges::transform(range, Out(b), [](int i) { return i * 2; });
+      assert(b[0] == 4);
+      assert(base(ret.in) == a + 1);
+      assert(base(ret.out) == b + 1);
+    }
+  }
+
+  { // check that the transform function and projection call counts are correct
+    {
+      int predCount = 0;
+      int projCount = 0;
+      auto pred = [&](int) { ++predCount; return 1; };
+      auto proj = [&](int) { ++projCount; return 0; };
+      int a[] = {1, 2, 3, 4};
+      std::array<int, 4> c;
+      std::ranges::transform(In1(a), Sent1(In1(a + 4)), Out(c.data()), pred, proj);
+      assert(predCount == 4);
+      assert(projCount == 4);
+      assert((c == std::array{1, 1, 1, 1}));
+    }
+    {
+      int predCount = 0;
+      int projCount = 0;
+      auto pred = [&](int) { ++predCount; return 1; };
+      auto proj = [&](int) { ++projCount; return 0; };
+      int a[] = {1, 2, 3, 4};
+      std::array<int, 4> c;
+      auto range = std::ranges::subrange(In1(a), Sent1(In1(a + 4)));
+      std::ranges::transform(range, Out(c.data()), pred, proj);
+      assert(predCount == 4);
+      assert(projCount == 4);
+      assert((c == std::array{1, 1, 1, 1}));
+    }
+  }
+  return true;
+}
+// clang-format on
+
+template <class Out>
+constexpr void test_iterator_in1() {
+  test_iterators<cpp17_input_iterator<int*>, Out, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  test_iterators<cpp20_input_iterator<int*>, Out, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  test_iterators<forward_iterator<int*>, Out, forward_iterator<int*>>();
+  test_iterators<bidirectional_iterator<int*>, Out, bidirectional_iterator<int*>>();
+  test_iterators<random_access_iterator<int*>, Out, random_access_iterator<int*>>();
+  test_iterators<contiguous_iterator<int*>, Out, contiguous_iterator<int*>>();
+  test_iterators<int*, Out, int*>();
+  // static_asserting here to avoid hitting the constant evaluation step limit
+  static_assert(test_iterators<cpp17_input_iterator<int*>, Out, sentinel_wrapper<cpp17_input_iterator<int*>>>());
+  static_assert(test_iterators<cpp20_input_iterator<int*>, Out, sentinel_wrapper<cpp20_input_iterator<int*>>>());
+  static_assert(test_iterators<forward_iterator<int*>, Out, forward_iterator<int*>>());
+  static_assert(test_iterators<bidirectional_iterator<int*>, Out, bidirectional_iterator<int*>>());
+  static_assert(test_iterators<random_access_iterator<int*>, Out, random_access_iterator<int*>>());
+  static_assert(test_iterators<contiguous_iterator<int*>, Out, contiguous_iterator<int*>>());
+  static_assert(test_iterators<int*, Out, int*>());
+}
+
+constexpr bool test() {
+  { // check that std::ranges::dangling is returned properly
+    std::array<int, 5> b;
+    std::same_as<std::ranges::in_out_result<std::ranges::dangling, int*>> auto ret =
+        std::ranges::transform(std::array{1, 2, 3, 5, 4}, b.data(), [](int i) { return i * i; });
+    assert((b == std::array{1, 4, 9, 25, 16}));
+    assert(ret.out == b.data() + b.size());
+  }
+
+  { // check that returning another type from the projection works
+    {
+      struct S { int i; int other; };
+      S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+      std::array<int, 4> b;
+      std::ranges::transform(a, a + 4, b.begin(), [](S s) { return s.i; });
+      assert((b == std::array{0, 1, 3, 10}));
+    }
+    {
+      struct S { int i; int other; };
+      S a[] = { S{0, 0}, S{1, 0}, S{3, 0}, S{10, 0} };
+      std::array<int, 4> b;
+      std::ranges::transform(a, b.begin(), [](S s) { return s.i; });
+      assert((b == std::array{0, 1, 3, 10}));
+    }
+  }
+
+  { // check that std::invoke is used
+    struct S { int i; };
+    S a[] = { S{1}, S{3}, S{2} };
+    std::array<int, 3> b;
+    auto ret = std::ranges::transform(a, b.data(), [](int i) { return i; }, &S::i);
+    assert((b == std::array{1, 3, 2}));
+    assert(ret.out == b.data() + 3);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test_iterator_in1<cpp17_output_iterator<int*>>();
+  test_iterator_in1<cpp20_output_iterator<int*>>();
+  test_iterator_in1<forward_iterator<int*>>();
+  test_iterator_in1<bidirectional_iterator<int*>>();
+  test_iterator_in1<random_access_iterator<int*>>();
+  test_iterator_in1<contiguous_iterator<int*>>();
+  test_iterator_in1<int*>();
+  test();
+  static_assert(test());
+
+  return 0;
+}