The TAP specification says that failing tests that are currently
expected to fail (like Automake's XFAIL) are to be reported as
"not ok", with that failure ignored as a result of the TODO
directive, with this example:

    not ok 3 - infinite loop # TODO halting problem unsolved

A test reported as "ok # TODO" indicates that something that is
expected to fail has unexpectedly succeeded, similar to Automake's
XPASS.

Signed-off-by: Simon McVittie <smcv@collabora.com>