Add unit tests for the tid allocator (#2519)

Add simple infrastructure to add more unit tests in the future. At the moment tests
are only executed on Linux, but can be extended to other platforms if needed.

Use https://github.com/google/googletest/ as a framework.

core/iwasm/libraries/lib-wasi-threads/unit-test/lib_wasi_threads_unit_tests.cmake

@@ -0,0 +1,6 @@
+# Copyright (C) 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+create_wamr_unit_test(wasi_threads
+    ${CMAKE_CURRENT_LIST_DIR}/test_tid_allocator.cpp
+)

core/iwasm/libraries/lib-wasi-threads/unit-test/test_tid_allocator.cpp

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2023 Amazon.com Inc. or its affiliates. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#include <gtest/gtest.h>
+
+#include "tid_allocator.h"
+
+#include <stdint.h>
+
+class TidAllocatorTest : public ::testing::Test
+{
+  protected:
+    void SetUp() override { ASSERT_TRUE(tid_allocator_init(&_allocator)); }
+
+    void TearDown() override { tid_allocator_deinit(&_allocator); }
+
+    TidAllocator _allocator;
+};
+
+static bool
+is_tid_valid(int32 tid)
+{
+    /* See: https://github.com/WebAssembly/wasi-threads#design-choice-thread-ids
+     */
+    return tid >= TID_MIN && tid <= TID_MAX;
+}
+
+TEST_F(TidAllocatorTest, BasicTest)
+{
+    int32 tid = tid_allocator_get_tid(&_allocator);
+
+    ASSERT_TRUE(is_tid_valid(tid));
+}
+
+TEST_F(TidAllocatorTest, ShouldFailOnAllocatingMoreThanAllowedThreadIDs)
+{
+    int32 last_tid = 0;
+    for (int32 i = 0; i < TID_MAX + 1; i++) {
+        last_tid = tid_allocator_get_tid(&_allocator);
+        if (last_tid < 0) {
+            break;
+        }
+        ASSERT_TRUE(is_tid_valid(last_tid));
+    }
+
+    ASSERT_LT(last_tid, 0);
+}
+
+TEST_F(TidAllocatorTest, ShouldAllocateMoreThanAllowedTIDsIfOldTIDsAreReleased)
+{
+    int32 last_tid = 0;
+    for (int32 i = 0; i < TID_MAX + 1; i++) {
+        if (last_tid != 0) {
+            tid_allocator_release_tid(&_allocator, last_tid);
+        }
+
+        last_tid = tid_allocator_get_tid(&_allocator);
+        ASSERT_TRUE(is_tid_valid(last_tid));
+    }
+}