New cop to disallow printing from tests

[kevinrobell-st]

Is your feature request related to a problem? Please describe.

We noticed some print debugging statements in test output. I assumed they were already covered by existing cops but they weren't.

Describe the solution you'd like

It'd be nice to have a cop similar to the existing Rails/Output cop that prevents print debugging in the test directory.

• https://docs.rubocop.org/rubocop-rails/cops_rails.html#railsoutput

Describe alternatives you've considered

Writing a custom cop.

Additional context

I could technically just change the Include: field on the Rails/Output cop to prevent this from happening in tests but the error message would then be unhelpful. I also assume this would be more generally applicable outside of my own project.

[pirj]

Can you give an example? Is this debugging output coming from the spec code, or the production code? Did you have in mind to scope this to Rails projects, or do you think this should apply to any Ruby project that uses RSpec?

[kevinrobell-st]

It's mostly to make sure that print debugging in tests never passes CI.

it "returns an empty response" do
  get endpoint, :params => params
-  puts response.parsed_body
  expect(response).to have_http_status(:ok)
end

It would only check for print statements in spec code and not in production code. I think it would be useful in general but maybe there's some project that relies on printing from tests that I don't know about.

[pirj]

This would indeed make a useful cop. Would you like to contribute it?
As for legitimate uses, it is possible to grep real-world-rspec repos

[kevinrobell-st]

Yeah, I'd be interested in working on it. Since there is a very similar cop that already exists, would it be fine to just modify the existing one and include the license from that repo as attribution? I didn't know about the real-world-* repos. They look very helpful for these sorts of projects.

[pirj]

We’re the same org, feel free to borrow the code from the other repo the way you want.

[Earlopain]

As for legitimate uses, it is possible to grep real-world-rspec repos

Output in specs themselves (like the given example), I'm unsure if there are valid use-cases. I know rails (which doesn't use rspec but the general idea is valid) prints some info about external dependencies outside of specs. Like if memcached/redis etc. is available or not. That seems a valid usecase.

[bquorning]

In one project, I have redirected $stdout (and sometimes $stderr) to a StringIO initialized with an immutable string (-""), so all printing will cause an error. So yes, I think this cop will be useful 😅

However most of the cases I catch come from people using a Logger instance initialized with $stdout/STDOUT. And the cop suggested in #2129 will unfortunately not catch such cases.