Elements are rendered when the 'display' attribute is set to any valid value other than 'none'.
For each valid 'display' value (except none), the test creates a 'rect' element with that 'display' value assigned. Under that element, a red 'rect' is placed at the exact same 'x', 'y' position with the same height and width. Test passes if the 'rect' with 'display' covers the red 'rect'.
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Test passes if 16 black rectangles are shown and there is no red visible on the page.