[tests/functional/test_cache] Use os.path.join() instead of hard-coding the path separator.

Author: duckinator

tests/functional/test_cache.py

@@ -86,9 +86,10 @@ def _remove_matches_wheel(wheel_name, result):
 
         # The "/arbitrary/pathname/" bit is an implementation detail of how
         # the `populate_wheel_cache` fixture is implemented.
-        expected = 'Removed {}/arbitrary/pathname/{}'.format(
-            wheel_cache_dir, wheel_filename,
+        path = os.path.join(
+            wheel_cache_dir, 'arbitrary', 'pathname', wheel_filename,
         )
+        expected = 'Removed {}'.format(path)
         return expected in lines
 
     return _remove_matches_wheel