Fix regex sorting issue from #391 (#392)

* Rename "helper_tests.py" to "test_helpers.py".

This causes it to get picked up by pytest, which makes clear the failure
that I will fix in a followup commit.

* Sort paths longest to shortest.

Previously, path sort length was inverted, with short paths before long
ones, this led to a path like `/*` being handled *before* a path like
`/foo/bar/baz`, which is exactly what we didn't want. This was tested,
but the test was misnamed and so wasn't picked up by pytest.

---------

Co-authored-by: joshuamorton <joshuamorton@google.com>

Author: joshuamorton

flask_cors/core.py

@@ -73,11 +73,11 @@ def parse_resources(resources):
         def sort_key(pair):
             pattern, _ = pair
             if isinstance(pattern, RegexObject):
-                return (1, 0, pattern.pattern.count("/"), -len(pattern.pattern))
+                return (1, 0, -pattern.pattern.count("/"), -len(pattern.pattern))
             elif probably_regex(pattern):
-                return (1, 1, pattern.count("/"), -len(pattern))
+                return (1, 1, -pattern.count("/"), -len(pattern))
             else:
-                return (0, 0, pattern.count("/"), -len(pattern))
+                return (0, 0, -pattern.count("/"), -len(pattern))
 
         return sorted(resources, key=sort_key)