--- a/testing/marionette/harness/marionette/runner/base.py
+++ b/testing/marionette/harness/marionette/runner/base.py
@@ -826,26 +826,25 @@ setReq.onerror = function() {
             else:
                 self.marionette.baseurl = self.server_root
                 self.logger.info("using remote content from %s" % self.marionette.baseurl)
 
     def _add_tests(self, tests):
         for test in tests:
             self.add_test(test)
 
-        invalid_tests = [t['filepath'] for t in self.tests if not self._is_filename_valid(t['filepath'], True)]
+        invalid_tests = [t['filepath'] for t in self.tests if not self._is_filename_valid(t['filepath'])]
         if invalid_tests:
             raise Exception("Test file names must be of the form "
                             "'test_something.py', 'test_something.js', or 'testSomething.js'."
                             " Invalid test names:\n  %s"
                             % '\n  '.join(invalid_tests))
 
-    def _is_filename_valid(self, filename, is_filepath=False):
-        if is_filepath:
-            filename = os.path.basename(filename)
+    def _is_filename_valid(self, filename):
+        filename = os.path.basename(filename)
         return self.filename_pattern.match(filename)
 
     def _log_skipped_tests(self):
         for test in self.manifest_skipped_tests:
             name = os.path.basename(test['path'])
             self.logger.test_start(name)
             self.logger.test_end(name,
                                  'SKIP',