Currently, for testing we simply run diff between expected output and the output generated on the instance being tested.

We should move to using pg_regress.
pg_regress is a binary available from postgres server dev packages. It is usually not added to $PATH, but is available under
$(pg_config --pkglibdir)/pgxs/src/test/regress/pg_regress. pg_regress calls diff under the hood, but advantages of pg_regress are:

The advantages of pg_regress are:

• Better edge-case handling (empty output, database unreachable, etc)
• Ability to ignore select failing tests
• Running tests in parallel
• Cross-platform (e.g. see Tests fail on WSL with no obvious difference in diffs #40 for an example platform issue, when using diff naively)