RSpec - How to compound matchers raise_error and output.to_stdout?

Question

I've got a Thor based ruby CLI project to which I'm trying to add unit testing. It started as a pet project and is now rather large and important internally. Anyway, I have never really started unit testing, only grafted onto existing examples, and so I'm very much a noob when it comes to rspec.

I'm starting with a rather basic example, making sure that if I give it a file that doesn't exist, that it replies with an explanatory error and exits.

Here's the ways I have tried to compound them:

context 'with incorrect filename' do
  it 'should fail cleanly' do
    expect do
      subject.format('bad_file_name')
    end.to output('   ERROR  Unable to load file bad_file_name, exiting...').to_stdout.and raise_error(SystemExit)
  end
end

which works but doesn't capture the stdout properly output here.. also tried:

context 'with incorrect filename' do
  it 'should fail cleanly' do
    expect do
      expect do
        subject.format('fixtures/invalid.yaml')
      end.to output('   ERROR  Unable to load file bad_file_name, exiting...').to_stdout
    end.to raise_error(SystemExit)
  end
end

Which looks like it works, except (as this example shows) it's not actually testing the output because that output wouldn't match.

So what's the right way to check both an error that was raised and the output to stdout at the same time?

Answer 1

this works for me

expect { whatever }.to output('stderr message').to_stderr
                   .and output(Regexp.new('stdout message')).to_stdout
                   .and raise_error('Error message')