js_checker.py: Restore smoke tests for linting violations.

PRESUBMIT_test_mocks.py

Index: PRESUBMIT_test_mocks.py
diff --git a/PRESUBMIT_test_mocks.py b/PRESUBMIT_test_mocks.py
index c269deec1fba066392fd1252ab30fac2715e4ea5..e2e43e35372700e182081d511d096f560625ae56 100644
--- a/PRESUBMIT_test_mocks.py
+++ b/PRESUBMIT_test_mocks.py
@@ -27,6 +27,7 @@ class MockInputApi(object):
     self.files = []
     self.is_committing = False
     self.change = MockChange([])
+    self.presubmit_local_path = os.path.dirname(__file__)
 
   def AffectedFiles(self, file_filter=None, include_deletes=False):
     return self.files
@@ -38,7 +39,7 @@ class MockInputApi(object):
     return self.files
 
   def PresubmitLocalPath(self):
-    return os.path.dirname(__file__)
+    return self.presubmit_local_path
 
   def ReadFile(self, filename, mode='rU'):
     if hasattr(filename, 'AbsoluteLocalPath'):