Tests: pathlib used where appropriate

Also fixed various pylint errors and style issues.

test/test_return.py

@@ -1,6 +1,7 @@
 import re
 
 import pytest
+
 from unit.applications.proto import ApplicationProto
 
 client = ApplicationProto()
@@ -90,7 +91,7 @@ def test_return_update():
 def test_return_location():
     reserved = ":/?#[]@!&'()*+,;="
     unreserved = (
-        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" "0123456789-._~"
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~"
     )
     unsafe = " \"%<>\\^`{|}"
     unsafe_enc = "%20%22%25%3C%3E%5C%5E%60%7B%7C%7D"