get the default `process.stdout.write` back after tests are finished

[stevemao]

I have a test which tests stdout so I need to change the default behaviour of process.stdout.

process.stdout.write = (function(write) {
    return function(string, encoding, fd) {
      var args = _.toArray(arguments);
      callback.call(callback, string);
    };
  }(process.stdout.write));

mocha's report, however, cannot be seen any more if I use this. It would be good if mocha remembers the default process.stdout.write at the beginning and change it back after tests are finished.

[estilles]

@stevemao, I had a similar issue with tests that require the changing the behavior of console.log(). IMO, I don't think the burden of restoring mocks/stubs/spies should fall on either Mocha or its reporters.

My solution was to create a "helper" function that saves the original console.log(), runs the test (which I pass as a function), and restores it upon completion. The following is a short, but functional, version of my solution. I omitted validation and other sanity checks for the sake of brevity.

module.exports = function helper(fn) {
  var originalConsoleLog = console.log;

  function restore() {
    console.log = originalConsoleLog;
  }

  if (fn.length) {
    fn(restore);
  else {
    fn();
    restore();
  }
}

Then ... in my tests I would ...

var helper = require('/path/to/helper');
...
describe('...', function() {
  // sync example
  it('should ...', function() {
    helper(function() {
      var logs[];
      console.log = function() { logs.push(arguments) }; // <-- or whatever you want to do
      assert(...);
      ...
    });
  });

  // async example
  it('should ...', function(done) {
    helper(function(restore) {
      var logs[];
      console.log = function() { logs.push(arguments) }; // <-- or whatever you want to do
      assert(...);

      asyncStuff(function() {
        assert(...);
        restore();
        done();
      });
    });
  });

});

This is just a rudimentary example, but I think you get the picture. You can easily adapt this to fit your particular use case.

[danielstjules]

I do roughly the same thing as @johnnyestilles for any CLI-related tools: https://github.com/danielstjules/jsinspect/blob/master/spec/helpers.js https://github.com/danielstjules/jsinspect/blob/master/spec/reporters/jsonSpec.js

Since I use node a lot for dev tools, I definitely have some bias towards saving a reference to process.stdout.write before tests, though @johnnyestilles is probably right in that it might be outside the scope of a test runner. However, it sure would be convenient! :)

[danielstjules]

The only reason I'd maybe lean towards having this behavior supported by Mocha is that you have to do cleanup from within a test, and can't rely on any hooks. So if your test errors out, you're not going to be able to restore process.stdout.write before mocha tries to print a line for the test case. It'll simply result in a missing line from the output, assuming your afterEach logic restores it.

[estilles]

@danielstjules, I do see your point. And, yes it would be very convenient (I do a lot of console.log/ process.stdout.write checks in my tests). So, is this something you guys would consider implementing? I'd be more than happy to work on it. :-)

[danielstjules]

That would be super helpful! I should probably ping someone else here, cause like I said, I'm a bit biased :)

cc @boneskull @dasilvacontin

[stevemao]

Each test should be sandboxed in mocha and users should be able to do whatever dodge things inside each test. Users can change process.stdout.write but they should still be able to see the report (although the report writes to process.stdout but this shouldn't concern users).

[danielstjules]

Alright, I'm convinced this is a good idea. :) @johnnyestilles If you'd like to submit a PR, feel free! Otherwise I might work on this tomorrow.

[estilles]

@danielstjules ... Already started working on one. Will submit it soon. :-)

[estilles]

@danielstjules, I went ahead and submitted my PR. It includes a module that I wrote a while back and am actively using in other projects, which happens to be a perfect fit for the issue @stevemao brought up. I included tests, but no docs (couldn't really find a place in the docs or the wiki where this could/should be documented). If you require docs for every PR just point me in the right direction and I'll write something up. :-)

[estilles]

@stevemao / @danielstjules, sorry ... I closed my PR. @a8m and @travisjeffery seem to think this is not a good idea.

@stevemao, it seems like your only recourse is to cleanup after yourself within each affected test, the same way I described in my initial comment.

[danielstjules]

This is in reference to #1601 (comment) & #1601 (comment) Figured it'd be better posted in this issue since the PR was closed.

@a8m @travisjeffery While I agree that proper dependency injection would go a long way, I feel like Mocha should at least maintain its own state. A spec shouldn't be able to break reporter output so easily. For example:

var assert = require('assert');

describe('example', function() {
  var output, write;

  write = process.stdout.write;

  beforeEach(function() {
    output = '';
    process.stdout.write = function(str) {
      output += str;
    };
  });

  afterEach(function() {
    process.stdout.write = write;
  });

  it('I feel like this is acceptable', function() {
    console.log('testing');
    assert.equal(output, 'testing\n');
  });
});

$ mocha example.js



  1 passing (4ms)

Note that there's no output because we modified stdout.write. Along the lines of promoting DI, an alternative to the PR @johnnyestilles submitted would be to apply it to Mocha's reporters. We could pass process.stdout.write into the reporters, caching the function, rather than invoking it directly (as seen in https://github.com/mochajs/mocha/blob/master/lib/reporters/dot.js)

[danielstjules]

@johnnyestilles Sorry about that. I'm hoping that something smaller in scope might work a bit better.