diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp
--- a/libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp
@@ -16,6 +16,7 @@
 
 #include <algorithm>
 #include <iterator>
+#include <numeric>
 #include <random>
 #include <cassert>
 
diff --git a/libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable.pass.cpp b/libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable.pass.cpp
--- a/libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable.pass.cpp
+++ b/libcxx/test/std/concepts/concepts.lang/concept.swappable/swappable.pass.cpp
@@ -150,7 +150,8 @@
 constexpr bool check_throwable_adl_swappable_arrays() {
   throwable_adl_swappable x[] = {{0}, {1}, {2}, {3}};
   throwable_adl_swappable y[] = {{4}, {5}, {6}, {7}};
-  return check_swap_22(x, y) && !noexcept(std::ranges::swap(x, y));
+  constexpr auto not_noexcept = !noexcept(std::ranges::swap(x, y));
+  return check_swap_22(x, y) && not_noexcept;
 }
 static_assert(check_throwable_adl_swappable_arrays());
 
diff --git a/libcxx/test/std/containers/sequences/vector.bool/reserve.pass.cpp b/libcxx/test/std/containers/sequences/vector.bool/reserve.pass.cpp
--- a/libcxx/test/std/containers/sequences/vector.bool/reserve.pass.cpp
+++ b/libcxx/test/std/containers/sequences/vector.bool/reserve.pass.cpp
@@ -13,6 +13,7 @@
 
 #include <vector>
 #include <cassert>
+#include <stdexcept>
 
 #include "test_macros.h"
 #include "min_allocator.h"
diff --git a/libcxx/test/std/containers/sequences/vector/access.pass.cpp b/libcxx/test/std/containers/sequences/vector/access.pass.cpp
--- a/libcxx/test/std/containers/sequences/vector/access.pass.cpp
+++ b/libcxx/test/std/containers/sequences/vector/access.pass.cpp
@@ -23,6 +23,7 @@
 
 #include <vector>
 #include <cassert>
+#include <stdexcept>
 
 #include "min_allocator.h"
 #include "test_macros.h"
@@ -39,7 +40,7 @@
 
 template <class Vector>
 void test_get_basic(Vector& c, int start_value) {
-    const int n = c.size();
+    const int n = static_cast<int>(c.size());
     for (int i = 0; i < n; ++i)
         assert(c[i] == start_value + i);
     for (int i = 0; i < n; ++i)
@@ -47,7 +48,7 @@
 
 #ifndef TEST_HAS_NO_EXCEPTIONS
     try {
-        c.at(n);
+        TEST_IGNORE_NODISCARD c.at(n);
         assert(false);
     } catch (const std::out_of_range&) {}
 #endif
diff --git a/libcxx/test/std/containers/sequences/vector/vector.capacity/reserve.pass.cpp b/libcxx/test/std/containers/sequences/vector/vector.capacity/reserve.pass.cpp
--- a/libcxx/test/std/containers/sequences/vector/vector.capacity/reserve.pass.cpp
+++ b/libcxx/test/std/containers/sequences/vector/vector.capacity/reserve.pass.cpp
@@ -12,6 +12,7 @@
 
 #include <vector>
 #include <cassert>
+#include <stdexcept>
 #include "test_macros.h"
 #include "test_allocator.h"
 #include "min_allocator.h"
diff --git a/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp b/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp
--- a/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp
@@ -22,12 +22,12 @@
 };
 
 constexpr int count(std::span<const Sink> sp) {
-    return sp.size();
+    return static_cast<int>(sp.size());
 }
 
 template<int N>
 constexpr int countn(std::span<const Sink, N> sp) {
-    return sp.size();
+    return static_cast<int>(sp.size());
 }
 
 constexpr bool test() {
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/cxx20_iter_member.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/cxx20_iter_member.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/cxx20_iter_member.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/cxx20_iter_member.pass.cpp
@@ -20,6 +20,10 @@
 
 #include "test_macros.h"
 
+#ifdef _MSC_VER
+#pragma warning (disable: 4244) // conversion from 'double' to 'NoIteratorAlias::value_type', possible loss of data
+#endif
+
 struct NoIteratorAlias {
     double data_[3] = {};
     using value_type = int;
diff --git a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.hash/hash.pass.cpp b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.hash/hash.pass.cpp
--- a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.hash/hash.pass.cpp
+++ b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.hash/hash.pass.cpp
@@ -30,10 +30,10 @@
 
 template <class C>
 void do_test(int *LHSVal, int *RHSVal) {
-  const size_t ExpectLHS = std::hash<void*>{}((LHSVal));
-  const size_t ExpectRHS = std::hash<void*>{}((RHSVal));
-  const C LHS = C::from_address((LHSVal));
-  const C RHS = C::from_address((RHSVal));
+  [[maybe_unused]] const size_t ExpectLHS = std::hash<void*>{}(LHSVal);
+  [[maybe_unused]] const size_t ExpectRHS = std::hash<void*>{}(RHSVal);
+  const C LHS = C::from_address(LHSVal);
+  const C RHS = C::from_address(RHSVal);
   const std::hash<C> h;
 
   LIBCPP_ASSERT(h(LHS) == ExpectLHS);
diff --git a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.export/from_address.pass.cpp b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.export/from_address.pass.cpp
--- a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.export/from_address.pass.cpp
+++ b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.export/from_address.pass.cpp
@@ -36,9 +36,9 @@
     assert(c.address() == &dummy);
   }
   {
-    C::from_address((int*)nullptr);
-    C::from_address((void*)nullptr);
-    C::from_address((char*)nullptr);
+    TEST_IGNORE_NODISCARD C::from_address((int*)nullptr);
+    TEST_IGNORE_NODISCARD C::from_address((void*)nullptr);
+    TEST_IGNORE_NODISCARD C::from_address((char*)nullptr);
   }
   {
     char dummy = 42;
diff --git a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp
--- a/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp
+++ b/libcxx/test/std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp
@@ -69,7 +69,7 @@
   assert(base);
   assert(base.done() == false);
 
-  h.promise();
+  TEST_IGNORE_NODISCARD h.promise();
   assert(h.address() == base.address());
   assert(h == base);
   assert(h.address() != nullptr);
diff --git a/libcxx/test/std/numerics/bit/byteswap.pass.cpp b/libcxx/test/std/numerics/bit/byteswap.pass.cpp
--- a/libcxx/test/std/numerics/bit/byteswap.pass.cpp
+++ b/libcxx/test/std/numerics/bit/byteswap.pass.cpp
@@ -43,6 +43,9 @@
     return {static_cast<T>(0xABCDFE9477936406), static_cast<T>(0x0664937794FECDAB)};
   }
   assert(false);
+#ifdef _MSC_VER
+  __assume(false); // *sigh* `assert` can return on MSVC - swear this one won't
+#endif
 }
 
 template <class T>
@@ -57,8 +60,8 @@
   test_num<uint32_t>(0x01234567, 0x67452301);
   test_num<uint64_t>(0x0123456789ABCDEF, 0xEFCDAB8967452301);
 
-  test_num<int8_t>(0xAB, 0xAB);
-  test_num<int16_t>(0xCDEF, 0xEFCD);
+  test_num<int8_t>(static_cast<int8_t>(0xAB), static_cast<int8_t>(0xAB));
+  test_num<int16_t>(static_cast<int16_t>(0xCDEF), static_cast<int16_t>(0xEFCD));
   test_num<int32_t>(0x01234567, 0x67452301);
   test_num<int64_t>(0x0123456789ABCDEF, 0xEFCDAB8967452301);
 
@@ -71,7 +74,7 @@
 
   test_num<bool>(true, true);
   test_num<bool>(false, false);
-  test_num<char>(0xCD, 0xCD);
+  test_num<char>(static_cast<char>(0xCD), static_cast<char>(0xCD));
   test_num<unsigned char>(0xEF, 0xEF);
   test_num<signed char>(0x45, 0x45);
   test_num<char8_t>(0xAB, 0xAB);
diff --git a/libcxx/test/std/ranges/range.factories/range.iota.view/range_concept_conformance.compile.pass.cpp b/libcxx/test/std/ranges/range.factories/range.iota.view/range_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/ranges/range.factories/range.iota.view/range_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/ranges/range.factories/range.iota.view/range_concept_conformance.compile.pass.cpp
@@ -21,10 +21,10 @@
 
   auto operator<=>(const Decrementable&) const = default;
 
-  constexpr Decrementable& operator++();
-  constexpr Decrementable  operator++(int);
-  constexpr Decrementable& operator--();
-  constexpr Decrementable  operator--(int);
+  Decrementable& operator++();
+  Decrementable  operator++(int);
+  Decrementable& operator--();
+  Decrementable  operator--(int);
 };
 
 struct Incrementable {
@@ -32,8 +32,8 @@
 
   auto operator<=>(const Incrementable&) const = default;
 
-  constexpr Incrementable& operator++();
-  constexpr Incrementable  operator++(int);
+  Incrementable& operator++();
+  Incrementable  operator++(int);
 };
 
 static_assert(std::ranges::random_access_range<std::ranges::iota_view<int>>);
diff --git a/libcxx/test/std/ranges/range.factories/range.iota.view/size.pass.cpp b/libcxx/test/std/ranges/range.factories/range.iota.view/size.pass.cpp
--- a/libcxx/test/std/ranges/range.factories/range.iota.view/size.pass.cpp
+++ b/libcxx/test/std/ranges/range.factories/range.iota.view/size.pass.cpp
@@ -65,7 +65,7 @@
   }
   {
     const std::ranges::iota_view<int, int> io(0, std::numeric_limits<int>::max());
-    assert(io.size() == std::numeric_limits<int>::max());
+    assert(io.size() == static_cast<unsigned int>(std::numeric_limits<int>::max()));
   }
 
   // Neither are integer like.
diff --git a/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp b/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.capacity/resize_and_overwrite.pass.cpp
@@ -14,6 +14,7 @@
 // void resize_and_overwrite(size_type n, Operation op)
 
 #include <cassert>
+#include <algorithm>
 #include <string>
 
 #include "make_string.h"
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/class.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/class.pass.cpp
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/class.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/class.pass.cpp
@@ -31,7 +31,7 @@
 void test() {
   using Context = std::basic_format_context<CharT*, CharT>;
   {
-    auto store = std::make_format_args<Context>();
+    [[maybe_unused]] auto store = std::make_format_args<Context>();
     LIBCPP_STATIC_ASSERT(
         std::is_same_v<decltype(store), std::__format_arg_store<Context>>);
     LIBCPP_STATIC_ASSERT(
@@ -40,7 +40,7 @@
     LIBCPP_ASSERT(store.__args.size() == 0);
   }
   {
-    auto store = std::make_format_args<Context>(1);
+    [[maybe_unused]] auto store = std::make_format_args<Context>(1);
     LIBCPP_STATIC_ASSERT(
         std::is_same_v<decltype(store), std::__format_arg_store<Context, int>>);
     LIBCPP_STATIC_ASSERT(
@@ -49,7 +49,7 @@
     LIBCPP_ASSERT(store.__args.size() == 1);
   }
   {
-    auto store = std::make_format_args<Context>(1, 'c');
+    [[maybe_unused]] auto store = std::make_format_args<Context>(1, 'c');
     LIBCPP_STATIC_ASSERT(
         std::is_same_v<decltype(store),
                        std::__format_arg_store<Context, int, char>>);
@@ -59,7 +59,7 @@
     LIBCPP_ASSERT(store.__args.size() == 2);
   }
   {
-    auto store = std::make_format_args<Context>(1, 'c', nullptr);
+    [[maybe_unused]] auto store = std::make_format_args<Context>(1, 'c', nullptr);
     LIBCPP_STATIC_ASSERT(
         std::is_same_v<decltype(store),
                        std::__format_arg_store<Context, int, char, std::nullptr_t>>);
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_format_args.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_format_args.pass.cpp
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_format_args.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_format_args.pass.cpp
@@ -25,10 +25,10 @@
 #include "test_macros.h"
 
 int main(int, char**) {
-  using Context = std::basic_format_context<
+  using Context [[maybe_unused]] = std::basic_format_context<
       std::back_insert_iterator<std::basic_string<char>>, char>;
 
-  auto value = std::make_format_args(42, nullptr, false, 1.0);
+  [[maybe_unused]] auto value = std::make_format_args(42, nullptr, false, 1.0);
 
   LIBCPP_ASSERT(value.__args.size() == 4);
   LIBCPP_ASSERT(test_basic_format_arg(value.__args[0], 42));
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_wformat_args.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_wformat_args.pass.cpp
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_wformat_args.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg.store/make_wformat_args.pass.cpp
@@ -25,10 +25,10 @@
 #include "test_macros.h"
 
 int main(int, char**) {
-  using Context = std::basic_format_context<
+  using Context [[maybe_unused]] = std::basic_format_context<
       std::back_insert_iterator<std::basic_string<wchar_t>>, wchar_t>;
 
-  auto value = std::make_wformat_args(42, nullptr, false, 1.0);
+  [[maybe_unused]] auto value = std::make_wformat_args(42, nullptr, false, 1.0);
 
   LIBCPP_ASSERT(value.__args.size() == 4);
   LIBCPP_ASSERT(test_basic_format_arg(value.__args[0], 42));
diff --git a/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/check_arg_id.pass.cpp b/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/check_arg_id.pass.cpp
--- a/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/check_arg_id.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/check_arg_id.pass.cpp
@@ -35,13 +35,14 @@
 void test_exception() {
   [] {
     std::format_parse_context context("", 1);
-    context.next_arg_id();
+    TEST_IGNORE_NODISCARD context.next_arg_id();
     try {
       context.check_arg_id(0);
       assert(false);
     } catch (const std::format_error& e) {
       LIBCPP_ASSERT(strcmp(e.what(), "Using manual argument numbering in automatic "
                                      "argument numbering mode") == 0);
+      (void) e;
       return;
     }
     assert(false);
diff --git a/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/next_arg_id.pass.cpp b/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/next_arg_id.pass.cpp
--- a/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/next_arg_id.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.formatter/format.parse.ctx/next_arg_id.pass.cpp
@@ -37,11 +37,12 @@
   context.check_arg_id(0);
 
   try {
-    context.next_arg_id();
+    TEST_IGNORE_NODISCARD context.next_arg_id();
     assert(false);
   } catch (const std::format_error& e) {
     LIBCPP_ASSERT(strcmp(e.what(), "Using automatic argument numbering in manual "
                                    "argument numbering mode") == 0);
+    (void) e;
     return;
   }
   assert(false);
diff --git a/libcxx/test/std/utilities/format/format.functions/format.pass.cpp b/libcxx/test/std/utilities/format/format.functions/format.pass.cpp
--- a/libcxx/test/std/utilities/format/format.functions/format.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.functions/format.pass.cpp
@@ -68,10 +68,10 @@
   }
   assert(false);
 #else
-  (void)what;
   (void)fmt;
   (void)sizeof...(args);
 #endif
+  (void)what;
 };
 
 int main(int, char**) {
diff --git a/libcxx/test/std/utilities/format/format.functions/format_tests.h b/libcxx/test/std/utilities/format/format.functions/format_tests.h
--- a/libcxx/test/std/utilities/format/format.functions/format_tests.h
+++ b/libcxx/test/std/utilities/format/format.functions/format_tests.h
@@ -164,7 +164,7 @@
       STR("hello {:{}}"), world, -1);
   check_exception(
       "A format-spec arg-id replacement exceeds the maximum supported value",
-      STR("hello {:{}}"), world, -1u);
+      STR("hello {:{}}"), world, ~0u);
   check_exception("Argument index out of bounds", STR("hello {:{}}"), world);
   check_exception(
       "A format-spec arg-id replacement argument isn't an integral type",
@@ -200,7 +200,7 @@
       STR("hello {:.{}}"), world, -1);
   check_exception(
       "A format-spec arg-id replacement exceeds the maximum supported value",
-      STR("hello {:.{}}"), world, -1u);
+      STR("hello {:.{}}"), world, ~0u);
   check_exception("Argument index out of bounds", STR("hello {:.{}}"), world);
   check_exception(
       "A format-spec arg-id replacement argument isn't an integral type",
diff --git a/libcxx/test/std/utilities/format/format.functions/vformat.locale.pass.cpp b/libcxx/test/std/utilities/format/format.functions/vformat.locale.pass.cpp
--- a/libcxx/test/std/utilities/format/format.functions/vformat.locale.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.functions/vformat.locale.pass.cpp
@@ -36,19 +36,21 @@
     std::string_view what, std::basic_string<CharT> fmt, const Args&... args) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
   try {
-    std::vformat(std::locale(), fmt,
-                 std::make_format_args<context_t<CharT>>(args...));
+    TEST_IGNORE_NODISCARD
+      std::vformat(std::locale(), fmt,
+                   std::make_format_args<context_t<CharT>>(args...));
     assert(false);
   } catch (std::format_error& e) {
     LIBCPP_ASSERT(e.what() == what);
+    (void)e;
     return;
   }
   assert(false);
 #else
-  (void)what;
   (void)fmt;
   (void)sizeof...(args);
 #endif
+  (void)what;
 };
 
 int main(int, char**) {
diff --git a/libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp b/libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp
--- a/libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp
@@ -35,18 +35,19 @@
     std::string_view what, std::basic_string<CharT> fmt, const Args&... args) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
   try {
-    std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...));
+    TEST_IGNORE_NODISCARD std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...));
     assert(false);
   } catch (std::format_error& e) {
     LIBCPP_ASSERT(e.what() == what);
+    (void)e;
     return;
   }
   assert(false);
 #else
-  (void)what;
   (void)fmt;
   (void)sizeof...(args);
 #endif
+  (void)what;
 };
 
 int main(int, char**) {
diff --git a/libcxx/test/std/utilities/format/format.functions/vformat_to.locale.pass.cpp b/libcxx/test/std/utilities/format/format.functions/vformat_to.locale.pass.cpp
--- a/libcxx/test/std/utilities/format/format.functions/vformat_to.locale.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.functions/vformat_to.locale.pass.cpp
@@ -76,14 +76,15 @@
     assert(false);
   } catch (std::format_error& e) {
     LIBCPP_ASSERT(e.what() == what);
+    (void)e;
     return;
   }
   assert(false);
 #else
-  (void)what;
   (void)fmt;
   (void)sizeof...(args);
 #endif
+  (void)what;
 };
 
 int main(int, char**) {
diff --git a/libcxx/test/std/utilities/format/format.functions/vformat_to.pass.cpp b/libcxx/test/std/utilities/format/format.functions/vformat_to.pass.cpp
--- a/libcxx/test/std/utilities/format/format.functions/vformat_to.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.functions/vformat_to.pass.cpp
@@ -76,14 +76,15 @@
     assert(false);
   } catch (std::format_error& e) {
     LIBCPP_ASSERT(e.what() == what);
+    (void)e;
     return;
   }
   assert(false);
 #else
-  (void)what;
   (void)fmt;
   (void)sizeof...(args);
 #endif
+  (void)what;
 };
 
 int main(int, char**) {
diff --git a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/explicit_const_optional_U.pass.cpp b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/explicit_const_optional_U.pass.cpp
--- a/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/explicit_const_optional_U.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.object/optional.object.ctor/explicit_const_optional_U.pass.cpp
@@ -73,7 +73,7 @@
 {
     int i_;
 public:
-    constexpr explicit Z(int i) : i_(i) { TEST_THROW(6);}
+    explicit Z(int i) : i_(i) {TEST_THROW(6);}
 
     friend constexpr bool operator==(const Z& x, const Z& y) {return x.i_ == y.i_;}
 };
diff --git a/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
--- a/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
@@ -380,7 +380,7 @@
   // Check that visit unambiguously picks the variant, even if the other base has __impl member.
   struct ImplVariantBase {
     struct Callable {
-      bool operator()();
+      bool operator()() { std::abort(); }
     };
 
     Callable __impl;
diff --git a/libcxx/test/std/utilities/variant/variant.visit/visit_return_type.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit/visit_return_type.pass.cpp
--- a/libcxx/test/std/utilities/variant/variant.visit/visit_return_type.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit/visit_return_type.pass.cpp
@@ -451,7 +451,7 @@
   // Check that visit unambiguously picks the variant, even if the other base has __impl member.
   struct ImplVariantBase {
     struct Callable {
-      bool operator()();
+      bool operator()() const { std::abort(); }
     };
 
     Callable __impl;
diff --git a/libcxx/test/support/charconv_test_helpers.h b/libcxx/test/support/charconv_test_helpers.h
--- a/libcxx/test/support/charconv_test_helpers.h
+++ b/libcxx/test/support/charconv_test_helpers.h
@@ -108,7 +108,7 @@
 
         // Poison the buffer for testing whether a successful std::to_chars
         // doesn't modify data beyond r.ptr.
-        std::iota(buf, buf + sizeof(buf), 1);
+        std::iota(buf, buf + sizeof(buf), char{1});
         r = to_chars(buf, buf + sizeof(buf), v, args...);
         assert(r.ec == std::errc{});
         for (size_t i = r.ptr - buf; i < sizeof(buf); ++i)
diff --git a/libcxx/test/support/test_constexpr_container.h b/libcxx/test/support/test_constexpr_container.h
--- a/libcxx/test/support/test_constexpr_container.h
+++ b/libcxx/test/support/test_constexpr_container.h
@@ -38,7 +38,7 @@
     constexpr const T& back() const { assert(size_ >= 1); return data_[size_-1]; }
 
     constexpr iterator insert(const_iterator pos, T t) {
-        int i = (pos - data_);
+        int i = static_cast<int>(pos - data_);
         if (i != size_) {
             std::move_backward(data_ + i, data_ + size_, data_ + size_ + 1);
         }