I just ran into a rather nasty bug. The TEST_ASSERT_DELTA() and TEST_ASSERT_DELTA_MSG() macros will happily accept the test if either a, b, or delta is NaN. In my opinion such a test should always fail. A simple fix would be to negate the test, i.e. change

if (((b) < (a) - (delta)) || ((b) > (a) + (delta)))

into

if (!(((b) >= (a) - (delta)) && ((b) <= (a) + (delta))))

since comparisons involving NaN will always return false (except for !=, but that is not relevant here).