Tests: Establish root Tests directory, move Userland/Tests there

With the goal of centralizing all tests in the system, this is a
first step to establish a Tests sub-tree. It will contain all of
the unit tests and test harnesses for the various components in the
system.

Tests/LibPthread/TestLibPthreadSpinLocks.cpp

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2021, Brian Gianforcaro <bgianf@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibPthread/pthread.h>
+#include <LibTest/TestCase.h>
+#include <unistd.h>
+
+TEST_CASE(spin_init_process_scope)
+{
+    {
+        pthread_spinlock_t lock {};
+        auto result = pthread_spin_init(&lock, PTHREAD_SCOPE_PROCESS);
+        EXPECT_EQ(0, result);
+        result = pthread_spin_destroy(&lock);
+        EXPECT_EQ(0, result);
+    }
+
+    {
+        pthread_spinlock_t garbage_lock { 0x1337 };
+        auto result = pthread_spin_init(&garbage_lock, PTHREAD_SCOPE_PROCESS);
+        EXPECT_EQ(0, result);
+        result = pthread_spin_destroy(&garbage_lock);
+        EXPECT_EQ(0, result);
+    }
+}
+
+TEST_CASE(spin_init_system_scope)
+{
+    pthread_spinlock_t lock {};
+    auto result = pthread_spin_init(&lock, PTHREAD_SCOPE_SYSTEM);
+    EXPECT_EQ(0, result);
+    pthread_spinlock_t garbage_lock { 0x99999 };
+    result = pthread_spin_init(&garbage_lock, PTHREAD_SCOPE_PROCESS);
+    EXPECT_EQ(0, result);
+}
+
+TEST_CASE(spin_lock)
+{
+    pthread_spinlock_t lock {};
+    auto result = pthread_spin_lock(&lock);
+    EXPECT_EQ(0, result);
+
+    // We should detect that this thread already holds this lock.
+    result = pthread_spin_lock(&lock);
+    EXPECT_EQ(EDEADLK, result);
+}
+
+TEST_CASE(spin_try_lock)
+{
+    {
+        pthread_spinlock_t lock {};
+        auto result = pthread_spin_trylock(&lock);
+        EXPECT_EQ(0, result);
+
+        result = pthread_spin_unlock(&lock);
+        EXPECT_EQ(0, result);
+    }
+
+    {
+        pthread_spinlock_t lock {};
+        auto result = pthread_spin_trylock(&lock);
+        EXPECT_EQ(0, result);
+
+        // We should detect that this thread already holds the lock.
+        result = pthread_spin_trylock(&lock);
+        EXPECT_EQ(EBUSY, result);
+    }
+}
+
+static void lock_from_different_thread(pthread_spinlock_t* lock)
+{
+    pthread_t thread_id {};
+    auto result = pthread_create(
+        &thread_id, nullptr, [](void* param) -> void* {
+            auto lock = (pthread_spinlock_t*)param;
+            pthread_spin_lock(lock);
+            return nullptr;
+        },
+        lock);
+    EXPECT_EQ(0, result);
+
+    result = pthread_join(thread_id, nullptr);
+    EXPECT_EQ(0, result);
+}
+
+TEST_CASE(spin_unlock)
+{
+    {
+        pthread_spinlock_t lock {};
+        auto result = pthread_spin_lock(&lock);
+        EXPECT_EQ(0, result);
+
+        result = pthread_spin_unlock(&lock);
+        EXPECT_EQ(0, result);
+    }
+
+    {
+        pthread_spinlock_t lock {};
+        lock_from_different_thread(&lock);
+
+        auto result = pthread_spin_unlock(&lock);
+        EXPECT_EQ(EPERM, result);
+    }
+}
+
+TEST_CASE(spin_destroy)
+{
+    {
+        pthread_spinlock_t lock {};
+        auto result = pthread_spin_lock(&lock);
+        EXPECT_EQ(0, result);
+
+        result = pthread_spin_destroy(&lock);
+        EXPECT_EQ(EBUSY, result);
+
+        result = pthread_spin_unlock(&lock);
+        EXPECT_EQ(0, result);
+    }
+
+    {
+        pthread_spinlock_t lock {};
+        lock_from_different_thread(&lock);
+
+        auto result = pthread_spin_destroy(&lock);
+        EXPECT_EQ(EBUSY, result);
+    }
+}