The font for this test case has an AAT Extended Glyph Metamorphosis Table with a single Contextual Glyph Substitution Subtable. Its finite-state machine contains one state. For glyphs glyphs A, B, C, and D, the machine executes the per-glyph substitution #0 on CurrentIndex on a transition that is also marked with the DontAdvance flag. The glyph substitution replaces A by B, B by C, C by D, and D by E.

The input string for this test is ABCDE. If your rendering system correctly implements Apple Advanced Typography, the finite-state machine should loop for each glyph in state 0 until it gets rewritten to E. The final result should be EEEEE.