[TASK] Add tests for Cache FileBackends
Besides adding unit tests covering the basic functionality of the
``SimpleFileBackend`` this change introduces tests for the recently
modified way of including PHP files via
Previously files where included within a try/catch block swallowing
errors in included PHP files.
With Ied1dd72d4d9035a6f7673ceb096cc908c767d80c the try/catch block
was removed for performance reasons, with the side-effect that errors
and exceptions are no longer silently skipped.
Releases: master, 3.0