Move _capture_stdout to a common place

The _capture_stdout method was duplicated in a couple different test
classes that all inherited from PolicyBaseTestCase.

This commit just moves the method into PolicyBaseTestCase and removes
the duplicate implementations across test classes.

Change-Id: Id62db9bb0e6f0e6d0d2917714302947415cb9829

oslo_policy/tests/base.py

@@ -16,10 +16,12 @@
 import codecs
 import os
 import os.path
+import sys
 
 import fixtures
 from oslo_config import fixture as config
 from oslotest import base as test_base
+from six import moves
 
 from oslo_policy import _checks
 from oslo_policy import policy
@@ -52,6 +54,10 @@ class PolicyBaseTestCase(test_base.BaseTestCase):
         with codecs.open(path, 'w', encoding='utf-8') as f:
             f.write(contents)
 
+    def _capture_stdout(self):
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', moves.StringIO()))
+        return sys.stdout
+
 
 class FakeCheck(_checks.BaseCheck):
     def __init__(self, result=None):

oslo_policy/tests/test_generator.py

@@ -10,13 +10,10 @@
 #    under the License.
 
 import operator
-import sys
 import warnings
 
-import fixtures
 import mock
 from oslo_config import cfg
-from six import moves
 import stevedore
 import testtools
 
@@ -50,10 +47,6 @@ class GenerateSampleYAMLTestCase(base.PolicyBaseTestCase):
         super(GenerateSampleYAMLTestCase, self).setUp()
         self.enforcer = policy.Enforcer(self.conf, policy_file='policy.yaml')
 
-    def _capture_stdout(self):
-        self.useFixture(fixtures.MonkeyPatch('sys.stdout', moves.StringIO()))
-        return sys.stdout
-
     def test_generate_loadable_yaml(self):
         extensions = []
         for name, opts in OPTS.items():
@@ -343,10 +336,6 @@ class GenerateSampleJSONTestCase(base.PolicyBaseTestCase):
         super(GenerateSampleJSONTestCase, self).setUp()
         self.enforcer = policy.Enforcer(self.conf, policy_file='policy.json')
 
-    def _capture_stdout(self):
-        self.useFixture(fixtures.MonkeyPatch('sys.stdout', moves.StringIO()))
-        return sys.stdout
-
     def test_generate_loadable_json(self):
         extensions = []
         for name, opts in OPTS.items():
@@ -530,10 +519,6 @@ class ListRedundantTestCase(base.PolicyBaseTestCase):
     def setUp(self):
         super(ListRedundantTestCase, self).setUp()
 
-    def _capture_stdout(self):
-        self.useFixture(fixtures.MonkeyPatch('sys.stdout', moves.StringIO()))
-        return sys.stdout
-
     def test_matched_rules(self):
         extensions = []
         for name, opts in OPTS.items():