TIL how to suppress log output in ExUnit tests

If a test triggers noisy log output, you can use ExUnit.CaptureLog.capture_log/2 to capture the noisy function:

import ExUnit.CaptureLog

test "logs a warning" do
  log = capture_log(fn ->
    MyApp.noisy_function()
  end)

  assert log =~ "something went wrong"
end

To silence logs for the whole test, use the @tag attribute:

@tag capture_log: true
test "something that logs warnings" do
  assert MyApp.noisy_function() == :ok
end

Or enable it globally for all tests in test/test_helper.exs:

ExUnit.start(capture_log: true)

In all cases, if a test fails, the captured logs are included in the failure report.