Escape whitespace only strings when diffing them on failed assertions

[nicoddemus]

Fix #3443

Here's how it looks:

    def test_stuff():
        a = u'\r\n'
>       assert a == u'\n'
E       AssertionError: assert '\r\n' == '\n'
E         Strings contain only whitespace, escaping them using repr()
E         - '\r\n'
E         ?  --
E         + '\n'

.tmp\test_rn.py:4: AssertionError

[coveralls]

Coverage increased (+0.02%) to 92.821% when pulling 413b1aa on nicoddemus:escape-whitespace-diffs into 08aed1a on pytest-dev:master.

[RonnyPfannschmidt]

i believe we should try to make this function name a bit more speaking

[nicoddemus]

That's the best I could come up with by reading the git blame message for the line in question... do you have a suggestion?

If we don't get a better name I think that's not a big deal TBH given that it is a local function, but definitely if we can get an improved name the better.

[RonnyPfannschmidt]

escape_for_readable_diff perhaps - its a bit tricky to name this one indeed

[nicoddemus]

I like it, updated!

[nicoddemus]

Anything else @RonnyPfannschmidt?

[RonnyPfannschmidt]

well done 👍