diff --git a/libc/test/src/sys/stat/CMakeLists.txt b/libc/test/src/sys/stat/CMakeLists.txt
@@ -2,6 +2,38 @@ add_libc_testsuite(libc_sys_stat_unittests)
 
 add_subdirectory(testdata)
 
+add_libc_unittest(
+  chmod_test
+  SUITE
+    libc_sys_stat_unittests
+  SRCS
+    chmod_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.fcntl
+    libc.include.sys_stat
+    libc.src.fcntl.open
+    libc.src.sys.stat.chmod
+    libc.src.unistd.close
+    libc.src.unistd.write
+)
+
+add_libc_unittest(
+  fchmod_test
+  SUITE
+    libc_sys_stat_unittests
+  SRCS
+    fchmod_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.fcntl
+    libc.include.sys_stat
+    libc.src.fcntl.open
+    libc.src.sys.stat.fchmod
+    libc.src.unistd.close
+    libc.src.unistd.write
+)
+
 add_libc_unittest(
   mkdirat_test
   SUITE

diff --git a/libc/test/src/sys/stat/chmod_test.cpp b/libc/test/src/sys/stat/chmod_test.cpp
@@ -0,0 +1,64 @@
+//===-- Unittests for chmod -----------------------------------------------===//
+//
+// 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/fcntl/open.h"
+#include "src/sys/stat/chmod.h"
+#include "src/unistd/close.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+TEST(LlvmLibcChmodTest, ChangeAndOpen) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
+  // The test file is initially writable. We open it for writing and ensure
+  // that it indeed can be opened for writing. Next, we close the file and
+  // make it readonly using chmod. We test that chmod actually succeeded by
+  // trying to open the file for writing and failing.
+  constexpr const char *TEST_FILE = "testdata/chmod.test";
+  const char WRITE_DATA[] = "test data";
+  constexpr ssize_t WRITE_SIZE = ssize_t(sizeof(WRITE_DATA));
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::write(fd, WRITE_DATA, sizeof(WRITE_DATA)), WRITE_SIZE);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::chmod(TEST_FILE, S_IRUSR), Succeeds(0));
+
+  // Opening for writing should fail.
+  EXPECT_EQ(__llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY), -1);
+  EXPECT_NE(errno, 0);
+  errno = 0;
+  // But opening for reading should succeed.
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_RDONLY);
+  EXPECT_GT(fd, 0);
+  EXPECT_EQ(errno, 0);
+
+  EXPECT_THAT(__llvm_libc::close(fd), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::chmod(TEST_FILE, S_IRWXU), Succeeds(0));
+}
+
+TEST(LlvmLibcChmodTest, NonExistentFile) {
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::chmod("non-existent-file", S_IRUSR), Fails(ENOENT));
+  errno = 0;
+}
diff --git a/libc/test/src/sys/stat/fchmod_test.cpp b/libc/test/src/sys/stat/fchmod_test.cpp
@@ -0,0 +1,64 @@
+//===-- Unittests for fchmod ----------------------------------------------===//
+//
+// 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/fcntl/open.h"
+#include "src/sys/stat/fchmod.h"
+#include "src/unistd/close.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+TEST(LlvmLibcChmodTest, ChangeAndOpen) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
+  // The test file is initially writable. We open it for writing and ensure
+  // that it indeed can be opened for writing. Next, we close the file and
+  // make it readonly using chmod. We test that chmod actually succeeded by
+  // trying to open the file for writing and failing.
+  constexpr const char *TEST_FILE = "testdata/fchmod.test";
+  const char WRITE_DATA[] = "test data";
+  constexpr ssize_t WRITE_SIZE = ssize_t(sizeof(WRITE_DATA));
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(__llvm_libc::write(fd, WRITE_DATA, sizeof(WRITE_DATA)), WRITE_SIZE);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  EXPECT_THAT(__llvm_libc::fchmod(fd, S_IRUSR), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  // Opening for writing should fail.
+  EXPECT_EQ(__llvm_libc::open(TEST_FILE, O_APPEND | O_WRONLY), -1);
+  EXPECT_NE(errno, 0);
+  errno = 0;
+  // But opening for reading should succeed.
+  fd = __llvm_libc::open(TEST_FILE, O_APPEND | O_RDONLY);
+  EXPECT_GT(fd, 0);
+  EXPECT_EQ(errno, 0);
+
+  EXPECT_THAT(__llvm_libc::fchmod(fd, S_IRWXU), Succeeds(0));
+  EXPECT_THAT(__llvm_libc::close(fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChmodTest, NonExistentFile) {
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::fchmod(-1, S_IRUSR), -1);
+  ASSERT_NE(errno, 0);
+  errno = 0;
+}
diff --git a/libc/test/src/sys/stat/testdata/CMakeLists.txt b/libc/test/src/sys/stat/testdata/CMakeLists.txt
@@ -1,2 +1,4 @@
-# This directory will be used to create test files and delete them
-# from tests.
+# This directory will be used to create test files.
+
+file(GENERATE OUTPUT chmod.test CONTENT "chmod test")
+file(GENERATE OUTPUT fchmod.test CONTENT "fchmod test")
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
@@ -2,6 +2,36 @@ add_libc_testsuite(libc_unistd_unittests)
 
 add_subdirectory(testdata)
 
+add_libc_unittest(
+  chdir_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    chdir_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.unistd
+    libc.src.fcntl.open
+    libc.src.unistd.chdir
+    libc.src.unistd.close
+    libc.test.errno_setter_matcher
+)
+
+add_libc_unittest(
+  fchdir_test
+  SUITE
+    libc_unistd_unittests
+  SRCS
+    fchdir_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.unistd
+    libc.src.fcntl.open
+    libc.src.unistd.fchdir
+    libc.src.unistd.close
+    libc.test.errno_setter_matcher
+)
+
 add_libc_unittest(
   read_write_test
   SUITE

diff --git a/libc/test/src/unistd/chdir_test.cpp b/libc/test/src/unistd/chdir_test.cpp
@@ -0,0 +1,47 @@
+//===-- Unittests for chdir -----------------------------------------------===//
+//
+// 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/fcntl/open.h"
+#include "src/unistd/chdir.h"
+#include "src/unistd/close.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+
+TEST(LlvmLibcChdirTest, ChangeAndOpen) {
+  // The idea of this test is that we will first open an existing test file
+  // without changing the directory to make sure it exists. Next, we change
+  // directory and open the same file to make sure that the "chdir" operation
+  // succeeded.
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_DIR = "testdata";
+  constexpr const char *TEST_FILE = "testdata/chdir.test";
+  constexpr const char *TEST_FILE_BASE = "chdir.test";
+  errno = 0;
+
+  int fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::chdir(TEST_DIR), Succeeds(0));
+  fd = __llvm_libc::open(TEST_FILE_BASE, O_PATH);
+  ASSERT_GT(fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChdirTest, ChangeToNonExistentDir) {
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::chdir("non-existent-dir"), Fails(ENOENT));
+  errno = 0;
+}
diff --git a/libc/test/src/unistd/fchdir_test.cpp b/libc/test/src/unistd/fchdir_test.cpp
@@ -0,0 +1,52 @@
+//===-- Unittests for fchdir ----------------------------------------------===//
+//
+// 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/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/fchdir.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+#include <fcntl.h>
+
+TEST(LlvmLibcChdirTest, ChangeAndOpen) {
+  // The idea of this test is that we will first open an existing test file
+  // without changing the directory to make sure it exists. Next, we change
+  // directory and open the same file to make sure that the "fchdir" operation
+  // succeeded.
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_DIR = "testdata";
+  constexpr const char *TEST_FILE = "testdata/fchdir.test";
+  constexpr const char *TEST_FILE_BASE = "fchdir.test";
+  errno = 0;
+
+  int dir_fd = __llvm_libc::open(TEST_DIR, O_DIRECTORY);
+  ASSERT_GT(dir_fd, 0);
+  ASSERT_EQ(errno, 0);
+  int file_fd = __llvm_libc::open(TEST_FILE, O_PATH);
+  ASSERT_GT(file_fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(file_fd), Succeeds(0));
+
+  ASSERT_THAT(__llvm_libc::fchdir(dir_fd), Succeeds(0));
+  file_fd = __llvm_libc::open(TEST_FILE_BASE, O_PATH);
+  ASSERT_GT(file_fd, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_THAT(__llvm_libc::close(file_fd), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::close(dir_fd), Succeeds(0));
+}
+
+TEST(LlvmLibcChdirTest, ChangeToNonExistentDir) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::fchdir(0), -1);
+  ASSERT_NE(errno, 0);
+  errno = 0;
+}
diff --git a/libc/test/src/unistd/testdata/CMakeLists.txt b/libc/test/src/unistd/testdata/CMakeLists.txt
@@ -1,4 +1,5 @@
-# This directory will be used to create test files and delete them
-# from tests.
+# This directory will be used to create test files.
 
 file(GENERATE OUTPUT lseek.test CONTENT "lseek test")
+file(GENERATE OUTPUT chdir.test CONTENT "chdir test")
+file(GENERATE OUTPUT fchdir.test CONTENT "fchdir test")