Add tests for sf::Clock

test/CMakeLists.txt

@@ -8,6 +8,7 @@ target_compile_features(sfml-test-main PRIVATE cxx_std_17)
 
 # System is always built
 SET(SYSTEM_SRC
+    "${SRCROOT}/System/Clock.cpp"
     "${SRCROOT}/System/FileInputStream.cpp"
     "${SRCROOT}/System/Time.cpp"
     "${SRCROOT}/System/Vector2.cpp"

test/System/Clock.cpp

@@ -0,0 +1,26 @@
+#include <SFML/System/Clock.hpp>
+#include "SystemUtil.hpp"
+#include <thread>
+
+#include <doctest.h>
+
+TEST_CASE("sf::Clock class - [system]")
+{
+    SUBCASE("getElapsedTime()")
+    {
+        const sf::Clock clock;
+        CHECK(clock.getElapsedTime() >= sf::microseconds(0));
+        const auto elapsed = clock.getElapsedTime();
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        CHECK(clock.getElapsedTime() > elapsed);
+    }
+
+    SUBCASE("restart()")
+    {
+        sf::Clock clock;
+        CHECK(clock.restart() >= sf::microseconds(0));
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        const auto elapsed = clock.restart();
+        CHECK(clock.restart() < elapsed);
+    }
+}