diff --git a/libc/test/src/unistd/dup2_test.cpp b/libc/test/src/unistd/dup2_test.cpp
@@ -0,0 +1,63 @@
+//===-- Unittests for dup -------------------------------------------------===//
+//
+// 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/dup2.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+  constexpr int DUPFD = 0xD0;
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_FILE = "testdata/dup.test";
+  int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  int dupfd = __llvm_libc::dup2(fd, DUPFD);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(dupfd, DUPFD);
+
+  // Write something via the dup
+  constexpr char WRITE_DATA[] = "Hello, dup!";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  ASSERT_EQ(ssize_t(WRITE_SIZE),
+            __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+  // Reopen the file for reading and create a dup.
+  fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  dupfd = __llvm_libc::dup2(fd, DUPFD);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(dupfd, DUPFD);
+
+  // Read the file content via the dup.
+  char buf[WRITE_SIZE];
+  ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+  ASSERT_STREQ(buf, WRITE_DATA);
+
+  // Verify that duping to the same fd value succeeds.
+  ASSERT_THAT(__llvm_libc::dup2(dupfd, dupfd), Succeeds(dupfd));
+
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::dup2(-1, 123), Fails(EBADF));
+}
diff --git a/libc/test/src/unistd/dup3_test.cpp b/libc/test/src/unistd/dup3_test.cpp
@@ -0,0 +1,69 @@
+//===-- Unittests for dup3 ------------------------------------------------===//
+//
+// 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/dup3.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+// The tests here are exactly the same as those of dup2. We only test the
+// plumbing of the dup3 syscall and not the dup3 functionality itself as it is
+// a simple syscall wrapper. Testing dup3 functionality is beyond the scope of
+// this test.
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+  constexpr int DUPFD = 0xD0;
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_FILE = "testdata/dup.test";
+  int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  int dupfd = __llvm_libc::dup3(fd, DUPFD, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(dupfd, DUPFD);
+
+  // Write something via the dup
+  constexpr char WRITE_DATA[] = "Hello, dup!";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  ASSERT_EQ(ssize_t(WRITE_SIZE),
+            __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+  // Reopen the file for reading and create a dup.
+  fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  dupfd = __llvm_libc::dup3(fd, DUPFD, 0);
+  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(dupfd, DUPFD);
+
+  // Read the file content via the dup.
+  char buf[WRITE_SIZE];
+  ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+  ASSERT_STREQ(buf, WRITE_DATA);
+
+  // Verify that, unlike dup2, duping to the same fd value with dup3 fails.
+  ASSERT_THAT(__llvm_libc::dup3(dupfd, dupfd, 0), Fails(EINVAL));
+
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::dup3(-1, 123, 0), Fails(EBADF));
+}
diff --git a/libc/test/src/unistd/dup_test.cpp b/libc/test/src/unistd/dup_test.cpp
@@ -0,0 +1,59 @@
+//===-- Unittests for dup -------------------------------------------------===//
+//
+// 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/dup.h"
+#include "src/unistd/read.h"
+#include "src/unistd/unlink.h"
+#include "src/unistd/write.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include "utils/testutils/FDReader.h"
+
+#include <errno.h>
+
+TEST(LlvmLibcdupTest, ReadAndWriteViaDup) {
+  errno = 0;
+  using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+  constexpr const char *TEST_FILE = "testdata/dup.test";
+  int fd = __llvm_libc::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  int dupfd = __llvm_libc::dup(fd);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(dupfd, 0);
+
+  // Write something via the dup
+  constexpr char WRITE_DATA[] = "Hello, dup!";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  ASSERT_EQ(ssize_t(WRITE_SIZE),
+            __llvm_libc::write(dupfd, WRITE_DATA, WRITE_SIZE));
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+
+  // Reopen the file for reading and create a dup.
+  fd = __llvm_libc::open(TEST_FILE, O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  dupfd = __llvm_libc::dup(fd);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(dupfd, 0);
+
+  // Read the file content via the dup.
+  char buf[WRITE_SIZE];
+  ASSERT_THAT(__llvm_libc::read(dupfd, buf, WRITE_SIZE), Succeeds(WRITE_SIZE));
+  ASSERT_STREQ(buf, WRITE_DATA);
+
+  ASSERT_THAT(__llvm_libc::close(dupfd), Succeeds(0));
+  ASSERT_THAT(__llvm_libc::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST(LlvmLibcdupTest, DupBadFD) {
+  using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+  ASSERT_THAT(__llvm_libc::dup(-1), Fails(EBADF));
+}