There's a weird edge case I saw on CI where when running the specs in the "one-by-one" style where [this](https://github.com/ruby/ruby/blob/448e0d6668d5df4f63a17db2063b31ed50c39d46/ext/date/lib/date/format.rb#L323) DateTime was loaded, but [this](https://github.com/ruby/ruby/blob/448e0d6668d5df4f63a17db2063b31ed50c39d46/ext/date/lib/date.rb#L1451) one was not.

Not entirely sure why this was happening, and not excited to debug it any further, but explicitly doing this require fixes the issue.