showDiff: don’t stringify strings + tests

[marcello3d]

The showDiff feature is stringifying strings as JSON, which flattens multi-line text with \n and surrounds them with quotes.

I refactored the code slightly to only call utils.stringify if the actual/expected values are not strings.

You can see the bug by running mocha on the following .js file:

var test = require('mocha').it
var assert = require('assert')

assert.AssertionError.prototype.showDiff = true

test('compare multiline strings', function(){
    assert.equal("foo\ncar", "foo\nbar");
});

Current (mocha 2.0.1) output:

  1)  compare multiline strings:

      AssertionError: "foo\ncar" == "foo\nbar"
      + expected - actual

      +"foo\nbar"
      -"foo\ncar"

After patch:

  1)  compare multiline strings:

      AssertionError: "foo\ncar" == "foo\nbar"
      + expected - actual

       foo
      +bar
      -car  

[dasilvacontin]

I've seen PRs for this already, although they didn't have tests (and that was probably the reason they aren't merged already).

I'll take a look at the PR later today.

[boneskull]

@marcello3d Why was err.showDiff removed from the conditional?

[marcello3d]

It's not, err.showDiff was being checked twice before, and only once now. It's easier to see in the side-by-side diff.

[boneskull]

good, thx

[dasilvacontin]

@boneskull Maybe it would be a good idea to bump, since this bug was causing problems to a few people.

[boneskull]

@dasilvacontin Yeah I want to bump soon, no time right now though.

[dasilvacontin]

@boneskull, sure. I could take care of it, if you are interested.

[marcello3d]

Thanks y'all. :-)

Getting back into mocha (hadn't tried it since 1.13.0), lots of nice touches.