Some of our tests were creating a psql event sink and expecting
it to report (or not report) certain kinds of errors. These tests
were ill-founded in a couple of ways:
1. Tests that required the Postgres driver were not loading it.
This led to spurious successes on tests that wanted "some error"
from the sink constructor, but didn't exercise the right path.
2. Tests that wanted a Postgres sink to succeed without a database.
These tests "passed" because they weren't actually establishing a
connection to the database, but if they had would have failed for
the lack of one.
To fix this:
- Load the postgres driver in tests that need it.
- Verify connectivity before reporting successful creation of a PSQL event sink.
- Remove tests that wanted a psql sink without a database, since that case
is already tested elsewhere.