[whalesalad]

If your CI DB is not 100% in parity with the real db -- you are setting yourself up for disaster. It is a false sense of security.

Same reason I wince when people say things like "we just use SQLite in tests, but our real db is mysql/psql/etc"

The test results have no merit if they are testing against a glorified mock.

[victorbjorklund]

You could have the fast tests that catch 99,9999% of the issues on feature branches and just run the real slow test before putting in prod.

[justincormack]

You can have fast tests and slow. Having fast tests to make progress working on features is important.