--- a/testing/web-platform/tests/webdriver/tests/set_window_rect.py
+++ b/testing/web-platform/tests/webdriver/tests/set_window_rect.py
@@ -226,16 +226,62 @@ def test_x_y_floats(session):
     assert value["y"] == 400
 
     response = set_window_rect(session, {"x": 300, "y": 450.5})
     value = assert_success(response)
     assert value["x"] == 300
     assert value["y"] == 450.5
 
 
+@pytest.mark.parametrize("rect", [
+    {},
+
+    {"width": None},
+    {"height": None},
+    {"width": None, "height": None},
+
+    {"x": None},
+    {"y": None},
+    {"x": None, "y": None},
+
+    {"width": None, "x": None},
+    {"width": None, "y": None},
+    {"height": None, "x": None},
+    {"height": None, "Y": None},
+
+    {"width": None, "height": None, "x": None, "y": None},
+
+    {"width": 200},
+    {"height": 200},
+    {"x": 200},
+    {"y": 200},
+    {"width": 200, "x": 200},
+    {"height": 200, "x": 200},
+    {"width": 200, "y": 200},
+    {"height": 200, "y": 200},
+])
+def test_no_change(session, rect):
+    """
+    13. If width and height are not null:
+
+    [...]
+
+    14. If x and y are not null:
+
+    [...]
+
+    15. Return success with the JSON serialization of the current
+    top-level browsing context's window rect.
+    """
+
+    original = session.window.rect
+    response = set_window_rect(session, rect)
+    assert_success(response, original)
+
+
     original = session.window.rect
 
 
 def test_fully_exit_fullscreen(session):
     """
     10. Fully exit fullscreen.
 
     [...]