tests: Do not rely on NoCloseFileProxy.close being called for coverage.

It is not in python3.

caucase/test.py

@@ -110,7 +110,7 @@ class NoCloseFileProxy(object):
   def __getattr__(self, name):
     return getattr(self._real_file, name)
 
-  def close(self):
+  def close(self): # pragma: no cover
     """
     Don't.
     """