[WIP] Skip UNIX-specific tests so they don't break Windows builds.

This PR is meant for discussion rather than merging straight away.

Some of the existing tests are clearly UNIX specific. I have created a new test group for them and excluded it explicitly from the tests.
Should I
  * move the tests to the Integration group
  * Find a way to decide at runtime whether the test should be executed based on the current platform
  * or make them pass on windows as well
Turns out the compare fails because of different path separators. Will fix in a separate PR. This file is off the list.