diff --git a/libc/test/src/stdbit/stdc_first_trailing_one_ui_test.cpp b/libc/test/src/stdbit/stdc_first_trailing_one_ui_test.cpp
@@ -0,0 +1,20 @@
+//===-- Unittests for stdc_first_trailing_one_ui -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_trailing_one_ui.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstTrailingOneUiTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ui(UINT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstTrailingOneUiTest, OneHot) {
+  for (unsigned i = 0U; i != UINT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ui(1U << i), i + 1);
+}
diff --git a/libc/test/src/stdbit/stdc_first_trailing_one_ul_test.cpp b/libc/test/src/stdbit/stdc_first_trailing_one_ul_test.cpp
@@ -0,0 +1,20 @@
+//===-- Unittests for stdc_first_trailing_one_ul -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_trailing_one_ul.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstTrailingOneUlTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ul(ULONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstTrailingOneUlTest, OneHot) {
+  for (unsigned i = 0U; i != ULONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ul(1UL << i), i + 1);
+}
diff --git a/libc/test/src/stdbit/stdc_first_trailing_one_ull_test.cpp b/libc/test/src/stdbit/stdc_first_trailing_one_ull_test.cpp
@@ -0,0 +1,20 @@
+//===-- Unittests for stdc_first_trailing_one_ull ------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_trailing_one_ull.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstTrailingOneUllTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ull(ULLONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstTrailingOneUllTest, OneHot) {
+  for (unsigned i = 0U; i != ULLONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_ull(1ULL << i), i + 1);
+}
diff --git a/libc/test/src/stdbit/stdc_first_trailing_one_us_test.cpp b/libc/test/src/stdbit/stdc_first_trailing_one_us_test.cpp
@@ -0,0 +1,20 @@
+//===-- Unittests for stdc_first_trailing_one_us -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_trailing_one_us.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstTrailingOneUsTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_us(USHRT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstTrailingOneUsTest, OneHot) {
+  for (unsigned i = 0U; i != USHRT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_trailing_one_us(1U << i), i + 1);
+}