Unit test failing

Thanks for the note about the overlap with #2525898: Depricated setFactoryMethod(). Update needed to support Symfony 3.0 in core (I'm the one who opened #2525898).

I suppose we should try to remove the overlap between those issues, either by closing #2525898 in favor of this issue, or by removing the common part of the patch in this issue. Either way is fine by me though I have a slight preference for the latter. My reasoning is that issue in #2525898 (the deprecated setFactoryMethod() exception) has ramifications not only for Libraries API tests but it also blocks testing on any other contrib project that declares it as a dependency, no matter what parts of the API that project uses. So addressing it in isolation may get it pushed through faster. That said, if a maintainer is willing to knock-out all the test failures in one go, all the better.

This patch (minus the hunk already committed in #2525898) would get Drupal\libraries\Tests\LibrariesUnitTest working again, which would be good. The thing is I don't think any of the test coverage from LibrariesUnitTest will really be applicable going forward as the static methods tested will possibly become obsolete. Anyway, I suppose committing this couldn't hurt anything and would help keep tests passing until we can officially remove the obsolete chunks.

Committed the relevant hunk. As noted earlier it looks like these tests will get replaced soon.