I recently started a new job where I’m working working on a large Phoenix app for the first time. Running tests, or even one test, is very slow. I discovered that this was, in part, due to a test alias that was re-creating the test database on each invocation of $ mix test. Then I realized: phx_new aliases the test task out of the box!

# mix.exs
defp aliases do
  # ...
  # Generated by phx_new:
  test: ["ecto.create --quiet", "ecto.migrate --quiet", "test"]
  # ...
end

My assumption is that this is for convenience when running async tests as each new test db will need to be setup and you could change the number of partitions. But, this begs the question: once a project grows very large, how are you supposed to sanely do TDD?

Of course I have ideas—I could rename that alias to something else, like test.all (or something better than that), add a test.prepare to set up a single test db for running non-async tests, and now the test task just runs tests and that would work. But I’m really curious to hear from others (if you’re out there!) who have faced this as well and how you dealt with it.

Thanks!