How do I test Rails logging from an Rspec feature spec?

Question

This question tells me how to test logger statements from RSpec model and controller specs. Unfortunately, it doesn't seem to work from a feature spec. With this code:

# controller.rb
def action
  logger.info 'foobar'
end

# spec.rb
scenario 'logging should work' do
  expect(Rails.logger).to receive(:info).with('foobar')
  visit action_path
end

I get the error:

 Failure/Error: visit action_path
   #<ActiveSupport::Logger:0x007ff45b6e5ad0> received :info with unexpected arguments
     expected: ("foobar")
          got: (no args)

The test.log file does not contain foobar , so it seems the test is failing immediately, before the controller action has a chance to complete.

Is there some way to use this expect(Rails.logger) syntax in a feature spec?

Answer 1

The Rails.logger.info method can take a string or a block. If you're invoking the block form then it will give this "got: (no args)" output.

For example

logger.info 'foobar'

...all on one line will call .info with a string, but if you do

logger.info
  "foobar foobar longer message so I'll put it on its own line"

split across two lines without brackets, then you're actually passing a block. Add some brackets...

logger.info(
  "foobar foobar longer message so I'll put it on its own line"
)

...and you're back to a string.

He says knowingly after bashing his head on this problem for a few hours :-)

Before realising that, I started figuring out how to mock the Rails.logger class. That might be a useful approach for you or others. Maybe you're calling with a block for some other reason (something to do with feature vs controller specs?), or maybe you can't change the calling code, in which case... something like this might be a useful starting point:

class LoggerMock < Object
  def initialize; end

  def info(progname = nil, &block)
    mock_info(block.call)
  end
end

and

logger_mock = LoggerMock.new
allow(Rails).to receive(:logger).and_return(logger_mock)
expect(logger_mock).to receive(:mock_info).with('foobar')