  movementX_sum += movementX;
                    movementY_sum += movementY;

                    screenX_delta = e.screenX - screenX_last;
                    screenY_delta = e.screenY - screenY_last;

                    movementX_Y_inside_window_Test.step(function() {
                        assert_equals(movementX, screenX_delta, "movementX = screen_delta");
                        assert_equals(movementY, screenY_delta, "movementY = screen_delta");
                    });

                    screenX_