diff --git a/libc/test/src/unistd/truncate_test.cpp b/libc/test/src/unistd/truncate_test.cpp
@@ -0,0 +1,67 @@
+//===-- Unittests for truncate --------------------------------------------===//
+//
+// 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/string_view.h"
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/read.h"
+#include "src/unistd/truncate.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+
+#include <errno.h>
+
+namespace cpp = __llvm_libc::cpp;
+
+TEST(LlvmLibcTruncateTest, CreateAndTruncate) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char TEST_FILE[] = "testdata/truncate.test";
+  constexpr const char WRITE_DATA[] = "hello, truncate";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  char buf[WRITE_SIZE];
+
+  // The test strategy is as follows:
+  //   1. Create a normal file with some data in it.
+  //   2. Read it to make sure what was written is actually in the file.
+  //   3. Truncate to 1 byte.
+  //   4. Try to read more than 1 byte and fail.
+  errno = 0;
+  int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(ssize_t(WRITE_SIZE),
+            __llvm_libc::write(fd, WRITE_DATA, WRITE_SIZE));
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(ssize_t(WRITE_SIZE), __llvm_libc::read(fd, buf, WRITE_SIZE));
+  ASSERT_EQ(cpp::string_view(buf), cpp::string_view(WRITE_DATA));
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::truncate(TEST_FILE, off_t(1)), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(ssize_t(1), __llvm_libc::read(fd, buf, WRITE_SIZE));
+  ASSERT_EQ(buf[0], WRITE_DATA[0]);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcTruncateTest, TruncateNonExistentFile) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(
+      __llvm_libc::truncate("non-existent-dir/non-existent-file", off_t(1)),
+      Fails(ENOENT));
+}