the evergreen team observes that timezones are handled differently with the new bson library relative to mgobson. I don't think there's a problem in terms of correctness, but it causes our tests to fail in ways that are irritating, and requires some context in order to fix.

I believe that mgobson converted time.Time back to the current time zone, and the new driver leaves them in UTC. This should be fully documented in any migration material, and potentially in the API documentation, but it might be nice to build/provide a set of codecs for compatibility mode, to reduce migration friction.