@CastLouis: What you mean by postgrex.ex? You need to change configuration *.exs file in /config directory. Depends on environment that you are working on you should apply configuration change in appropriate configuration file like: test.exs.
Example config/test.exs file:
use Mix.Config
config :my_app, MyApp.Repo,
adapter: Ecto.Adapters.Postgres,
database: "my_app_test",
hostname: "localhost",
ownership_timeout: 60_000, # <- add this line
password: "postgres",
pool: Ecto.Adapters.SQL.Sandbox,
username: "postgres"
