Phoenix: Enable SQL logging in the test environment

This is obvious in hindsight, but I am writing this note in hopes that will help someone else.

I was looking for a way to see the SQL statements issued by my tests. I wasn't sure if that was something to be configured in ecto or postgrex.

Turns out, it is a phoenix configuration.

# config/test.exs
# ...
config :logger, level: :debug  
# ...

Thanks to Adam Rutkowski from the Phoenix Slack channel.