def METHOD_NAME(page, port):
    grid = Column(GridBox(
        Spacer(sizing_mode='stretch_width', height=50),
        Spacer(sizing_mode='stretch_width', height=50),
        Spacer(sizing_mode='stretch_width', height=50),
        ncols=2, sizing_mode='stretch_width'
    ), width=800)
    serve(grid, port=port, threaded=True, show=False)
    time.sleep(0.2)
    page.goto(f"http://localhost:{port}")
    bbox = page.locator(".bk-GridBox").bounding_box()
    children = page.locator(".bk-GridBox div")
    assert bbox['width'] == 800
    assert bbox['height'] == 100
    bbox1 = children.nth(0).bounding_box()
    assert bbox1['x'] == 0
    assert bbox1['width'] == 400
    assert bbox1['height'] == 50
    bbox2 = children.nth(1).bounding_box()
    assert bbox2['x'] == 400
    assert bbox2['width'] == 400
    assert bbox2['height'] == 50
    bbox3 = children.nth(2).bounding_box()
    assert bbox3['x'] == 0
    assert bbox3['width'] == 400
    assert bbox3['height'] == 50