Fix failing tests around DS on different OS

Currently all those tests file on windows due to at least one DS in there that has the wrong direction 
`\` vs `/`.
Since both slashes work, though, it is just cosmetics and only make the tests fail.
This PR resolves it by adding assertPathEquals() which unifies the path DS prior to comparing them.

The alternative would be either fixing it in the app (more str_replace necessary) or in the tests (more replace overhead there cloaking the actual test functionality).