This is testing whatever it *was* testing – in the original test, it was testing that `seconds.since(@now)` should equal `@now + seconds`. Now that I changed the original test to `seconds.seconds.since(@now)`, it goes through a different code path (it's now testing `AS::Duration#since` instead), and the original code path (`Numeric#since`) is untested. Hence the duplication (and also why I changed Numeric#since to use AS::Duration in the first pass)