Change tests to use actual temporary files.
Change tests to use actual temporary files.

The previous tests used mock and patched os.path.isfile, i.e. made assumptions about how the code works instead of actually testing that it does what it needs to.
These tests are more robust and are actually necessary since soon the way that file existence is checked will be changed to not use os.path.isfile.
The tests have been tested, i.e. the current method still passes the test, but it fails if modified incorrectly.

yola/healthcheck