Add coverage badge to README

[kshyatt]

As suggested in #9493.

[kshyatt]

Sorry, I forgot to put [ci skip] on this!

[IainNZ]

No problem, I was thinking about the CI too!

[dhoegh]

The badge do not lead to the same site as: https://coveralls.io/r/JuliaLang/julia. Which then do show a lower and older coverage number than Julia and @kshyatt work deserves.

[ViralBShah]

I verified - the link is not doing the right thing. It takes us to some older commits. How to fix this?

[kshyatt]

I did exactly what Coveralls told me to! Grrrrr. I think there's a larger issue where the Repo Stats part of our Coveralls.io page is doing something funky.

E: This is related to this issue I opened at CoverageBase. The correct commit information is not making it to Coveralls from the buildbot and so the repo stats aren't being updated. Interestingly, when I run the same script at julia.mit.edu, everything works fine. @staticfloat and @tkelman, do you have any thoughts?

[staticfloat]

Yes, @kshyatt is right. It's because the commit information isn't surviving all the way through to Coveralls. I remember having some serious headaches trying to figure out how to bully Coveralls into accepting my git commit information, looks like it's time to revisit it and figure out what's broken.

The OpenStack cluster at MIT had an emergency poweroff this morning due to coolant systems failing at CSAIL; so I'll take a look at this once the buildbots are back up.

[tkelman]

I don't have anything to add to this issue except to wholeheartedly second the sentiment behind

lower and older coverage number than Julia and @kshyatt work deserves.

[staticfloat]

@kshyatt can you give me the exact command sequence you're using to upload to your coveralls stats?

[tkelman]

Is it expected that in the "Gather inlined test results" and "Gather non-inlined test results" steps of http://buildbot.e.ip.saba.us:8010/builders/coverage_ubuntu14.04-x64/builds/544, that all of the .cov files are being Skipped?

[IainNZ]

Yep, its just because Coverage.jl does a silly thing where it walks through every file in the folder and looks for file.cov - so it works for the .jl files, but when it hits a .cov file it can't find a .cov.cov so it says "skipped".

[kshyatt]

Just a quick update, thanks to the amazing work of @staticfloat, the coverage badge is now correct!

[tkelman]

Nice work. I bet running the pkg test during the coverage run would make the numbers a bit better.

[staticfloat]

Yes, I briefly discussed the best way to do that with Tim Holy here, I'll write something up and see if we can't get it running tonight. :D