[Review]: Test map sources (#664)

I'll be adding tests to classes in map/sources in this PR (issue #664 ). What I have now is by no means the final result, and more stuff will be added in due time.
This is going to be one long PR!
You mean 'commented'? Those asserts cause problems on Travis. I guess the
floating point values differ slightly and are never exactly the same. It
was @dpshelio 's idea that I should compute the values first and test
against those (rightly so).
The commented asserts you see are a result of that idea. But it doesn't
seem to cut it in this case, and hence I commented them out.