gecko-dev/testing/web-platform/tests/webdriver/contexts.py

def test_resize(session):
    # setting the window size by webdriver is synchronous
    # so we should see the results immediately

    session.window.size = (200, 100)
    assert session.window.size == {"width": 100, "height": 200}

    session.window.size = (100, 200)
    assert session.window.size == {"width": 200, "height": 100}

def test_resize_by_script(session):
    # setting the window size by JS is asynchronous
    # so we poll waiting for the results

    size0 = session.window.size

    session.execute_script("window.resizeTo(100, 200)")
    size1 = session.window.size
    while size0 == size1:
        size1 = session.window.size
    assert size1 == {"width": 100, "height": 200}

    session.execute_script("window.resizeTo(200, 100)")
    size2 = session.window.size
    while size1 == size2:
        size2 = session.window.size
    assert size2 == {"width": 200, "height": 100}