The font for this test case is a variation font with a single axis. While the ‘gvar’ table does a regular interpolation without any special quirks, the font’s ‘avar’ table defines a mapping that modifies the variation axis.

A correct implementation should produce the test glyph in its maximally thin shape at axis value 100. The resulting glyph should become bolder until 250, then stay at the exact same weight until 650, then become bolder up to the maximum at 900.