Add extra time checks.

test/time/test_time.c

@@ -111,6 +111,17 @@ static void test_timeUpdate(void **state) {
   assert_float_equal(TIME.dynamicTime, TIME_STEP + 0.104f, 0.0001f);
   assert_float_equal(TIME.delta, TIME_STEP, 0.0001f); 
   assert_float_equal(TIME.time, TIME_STEP * 5, 0.0001f);
+
+  // Time can stand still if needed
+  SDL_GETTICKS_CALLED = false;
+  SDL_GETTICKS_TICKS = 104; // No time elapsed
+  timeUpdate();
+  assert_true(SDL_GETTICKS_CALLED);
+
+  // Time cannot go backwards
+  SDL_GETTICKS_TICKS = 90;
+  SDL_GETTICKS_CALLED = false;
+  expect_assert_failure(timeUpdate());
 }
 
 int main(int argc, char **argv) {