Unicode defines Standardized Variants of certain characters, including some Mathematical Symbols. The font for this test case contains a type 14 ‘cmap’ table that implements both the regular symbol ≩ U+2269 GREATER-THAN BUT NOT EQUAL TO, and its variant U+2269 U+FE00 GREATER-THAN BUT NOT EQUAL TO WITH VERTICAL STROKE. With a correct implementation, the two glyphs should look different. If the two glyphs look the same, or if you see any black boxes in the renderings, it’s a sign that your implementation is broken.