When testing for errors, you can use ExUnit.CaptureLog to capture log messages (which then won’t appear in the output).

In general, I wouldn’t advise muting errors in tests, since they might be indicative of why some tests are failing.

You can use only in the test that triggers Log output the @moduletag directive:

@moduletag :capture_log
test "Test that trigger log output..." do
  ...
end

The test config (config/test.exs) generated by mix phx.new has this.

# Print only warnings and errors during test
config :logger, level: :warn

for other kinds of outputs, capture_io/1 might help cleanup test output: https://hexdocs.pm/ex_unit/ExUnit.CaptureIO.html

This is … a good point. I have changed my config to the following:

# Print only warnings and errors during test
config :logger, level: :warn

As @jola suggested. This should do it, even though I may see some logs I don’t want to, I think the compromise is fair.