diff --git a/libc/test/src/__support/threads/thread_detach_test.cpp b/libc/test/src/__support/threads/thread_detach_test.cpp
@@ -0,0 +1,52 @@
+//===-- Unittests for thrd_t ----------------------------------------------===//
+//
+// 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/threads/mutex.h"
+#include "src/__support/threads/thread.h"
+#include "src/__support/threads/thread_attrib.h"
+#include "utils/UnitTest/Test.h"
+
+__llvm_libc::Mutex mutex(false, false, false);
+
+int func(void *) {
+  mutex.lock();
+  mutex.unlock();
+  return 0;
+}
+
+TEST(LlvmLibcTestThreadTest, DetachSimpleTest) {
+  mutex.lock();
+  __llvm_libc::Thread<int> th;
+  th.run(func, nullptr, nullptr, 0);
+
+  // Since |mutex| is held by the current thread, we guarantee that
+  // th is running and hence it is safe to detach. Since the thread is
+  // still running, it should be simple detach.
+  ASSERT_EQ(th.detach(), int(__llvm_libc::DetachType::SIMPLE));
+
+  // We will release |mutex| now to let the thread finish an cleanup itself.
+  mutex.unlock();
+}
+
+TEST(LlvmLibcTestThreadTest, DetachCleanupTest) {
+  mutex.lock();
+  __llvm_libc::Thread<int> th;
+  ASSERT_EQ(0, th.run(func, nullptr, nullptr, 0));
+
+  // Since |mutex| is held by the current thread, we will release it
+  // to let |th| run.
+  mutex.unlock();
+
+  // We will wait for |th| to finish. Since it is a joinable thread,
+  // we can wait on it safely.
+  th.wait();
+
+  // Since |th| is now finished, detaching should cleanup the thread
+  // resources.
+  ASSERT_EQ(th.detach(), int(__llvm_libc::DetachType::CLEANUP));
+}