It appears as though there were a series of regressions in bats between the old version 0.4.0 and the new community-managed one. umoci in particular fails under bats 1.1.0 with some very odd $output related failures. I'm going to look into this more, just opening it to make sure I don't forget. (I hit this while trying to test #172 with umoci to see the speed improvement, but then noticed a bunch of my tests were failing for no good reason.)