Move tests to relevant subprojects (#615)

- Moved test projects to the parent project they belong to
- Improved test stability/corectness
- Improved recursive directory deletion by safely ignoring current- and parent-directory entries.
- Update docs

TactilityKernel/tests/source/mutex_test.cpp

@@ -0,0 +1,67 @@
+#include "doctest.h"
+#include <tactility/concurrent/mutex.h>
+
+TEST_CASE("mutex_construct and mutex_destruct should properly set the handle") {
+    Mutex mutex = { 0 };
+    mutex_construct(&mutex);
+    CHECK_NE(mutex.handle, nullptr);
+    mutex_destruct(&mutex);
+    CHECK_EQ(mutex.handle, nullptr);
+}
+
+TEST_CASE("mutex_is_locked should return true only when the mutex is locked") {
+    Mutex mutex = { 0 };
+    mutex_construct(&mutex);
+
+    CHECK_EQ(mutex_is_locked(&mutex), false);
+    mutex_lock(&mutex);
+    CHECK_EQ(mutex_is_locked(&mutex), true);
+    mutex_unlock(&mutex);
+    CHECK_EQ(mutex_is_locked(&mutex), false);
+
+    mutex_destruct(&mutex);
+}
+
+TEST_CASE("mutex_try_lock should succeed on first lock but not on second") {
+    Mutex mutex = { 0 };
+    mutex_construct(&mutex);
+
+    CHECK_EQ(mutex_try_lock(&mutex, 0), true);
+    CHECK_EQ(mutex_try_lock(&mutex, 0), false);
+    mutex_unlock(&mutex);
+
+    mutex_destruct(&mutex);
+}
+
+TEST_CASE("mutex_lock in another task should block when a lock is active") {
+    static int task_lock_counter = 0;
+    Mutex mutex = { 0 };
+    task_lock_counter = 0;
+
+    mutex_construct(&mutex);
+    mutex_lock(&mutex);
+
+    TaskHandle_t task_handle;
+    auto task_create_result = xTaskCreate(
+        [](void* input) {
+            Mutex* mutex_ptr = static_cast<Mutex*>(input);
+            mutex_lock(mutex_ptr);
+            task_lock_counter++;
+            mutex_unlock(mutex_ptr);
+            vTaskDelete(nullptr);
+        },
+        "mutex_test",
+        2048,
+        &mutex,
+        0,
+        &task_handle
+    );
+
+    CHECK_EQ(task_create_result, pdPASS);
+    CHECK_EQ(task_lock_counter, 0);
+
+    mutex_unlock(&mutex);
+    vTaskDelay(2); // 1 is sufficient most of the time, but not always
+    CHECK_EQ(task_lock_counter, 1);
+    mutex_destruct(&mutex);
+}