The font for this test case contains a Horizontal Metrics Variation Table whose offsetToAdvanceWidthMapping field is zero. The font, which was kindly contributed by Adobe Systems, had triggered a bug in an unreleased version of the FreeType library; see FreeType bug 50170. If your implementation is correct, the advance width should grow as the weight increases. In particular, the letters A and B should not overlap, not even in the boldest weights. If you see any overlapping glyphs, your implementation fails to compute advance widths for fonts whose HVAR table contains no advance width mapping.