Fix yaql / json_pp deprecation warning

By default deprecationwarnings only trigger once per invocation,
so this test dependent strongly on execution order of all the tests
to pass. by enforcing warnings to be enabled while recording for
deprecationwarnings we can make this more reliable.

Change-Id: I657786b8c73488203f8b056adc65df77e084ec85

mistral/tests/unit/expressions/test_yaql_expression.py

@@ -16,6 +16,7 @@
 
 import datetime
 import json
+import sys
 import warnings
 
 import mock
@@ -139,6 +140,10 @@ class YaqlEvaluatorTest(base.BaseTest):
 
     def test_function_json_pp_deprecation(self):
         with warnings.catch_warnings(record=True) as w:
+            # ensure warnings aren't suppressed from other tests
+            for name, mod in list(sys.modules.items()):
+                getattr(mod, '__warningregistry__', dict()).clear()
+            warnings.simplefilter('always')
             result = self._evaluator.evaluate('json_pp($)', '3')
             self.assertEqual('"3"', result)
         self.assertEqual(len(w), 1)