Create CaptureOutput fixture

Add a fixture for controlling whether or not stdout and stderr are
captured as the test runs.

Blueprint oslotest-refactor-test-base-class

Change-Id: Ifa8d991c1a8e3ec643e5350d09fcb3895ac8378e

doc/source/api.rst

@@ -23,6 +23,12 @@ oslotest.moxstubout
 .. automodule:: oslotest.moxstubout
    :members:
 
+oslotest.output
+===================
+
+.. automodule:: oslotest.output
+   :members:
+
 oslotest.timeout
 ================
 

oslotest/base.py

@@ -20,6 +20,7 @@ import os
 import tempfile
 
 import fixtures
+from oslotest import output
 from oslotest import timeout
 
 import six
@@ -101,12 +102,7 @@ class BaseTestCase(testtools.TestCase):
         self.useFixture(timeout.Timeout())
 
     def _fake_output(self):
-        if os.environ.get('OS_STDOUT_CAPTURE') in _TRUE_VALUES:
-            stdout = self.useFixture(fixtures.StringStream('stdout')).stream
-            self.useFixture(fixtures.MonkeyPatch('sys.stdout', stdout))
-        if os.environ.get('OS_STDERR_CAPTURE') in _TRUE_VALUES:
-            stderr = self.useFixture(fixtures.StringStream('stderr')).stream
-            self.useFixture(fixtures.MonkeyPatch('sys.stderr', stderr))
+        self.output_fixture = self.useFixture(output.CaptureOutput())
 
     def _fake_logs(self):
         level = None

oslotest/output.py

@@ -0,0 +1,55 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import os
+
+import fixtures
+
+_TRUE_VALUES = ('True', 'true', '1', 'yes')
+
+
+class CaptureOutput(fixtures.Fixture):
+    """Optionally capture the output streams.
+
+    The behavior is managed through two environment variables. If
+    ``OS_STDOUT_CAPTURE`` is true then stdout is captured and if
+    ``OS_STDERR_CAPTURE`` is true then stderr is captured.
+
+    "True" values include ``True``, ``true``, ``1``, and ``yes``.
+
+    .. py:attribute:: stdout
+
+       The ``stream`` attribute from a :class:`StringStream` instance
+       replacing stdout.
+
+    .. py:attribute:: stderr
+
+       The ``stream`` attribute from a :class:`StringStream` instance
+       replacing stderr.
+
+    """
+
+    def __init__(self):
+        super(CaptureOutput, self).__init__()
+        self.stdout = None
+        self.stderr = None
+
+    def setUp(self):
+        super(CaptureOutput, self).setUp()
+        if os.environ.get('OS_STDOUT_CAPTURE') in _TRUE_VALUES:
+            self._stdout_fixture = fixtures.StringStream('stdout')
+            self.stdout = self.useFixture(self._stdout_fixture).stream
+            self.useFixture(fixtures.MonkeyPatch('sys.stdout', self.stdout))
+        if os.environ.get('OS_STDERR_CAPTURE') in _TRUE_VALUES:
+            self._stderr_fixture = fixtures.StringStream('stderr')
+            self.stderr = self.useFixture(self._stderr_fixture).stream
+            self.useFixture(fixtures.MonkeyPatch('sys.stderr', self.stderr))

tests/unit/test_base.py

@@ -99,6 +99,22 @@ class TestBaseTestCase(testtools.TestCase):
         # check that mock patches are cleaned up
         self.assertEqual(obj.value, obj.backup)
 
+    @mock.patch('os.environ')
+    def test_capture_output_disabled(self, mock_env):
+        mock_env.get.return_value = ''
+        tc = self.FakeTestCase("test_fake_test")
+        tc.setUp()
+        self.assertIs(None, tc.output_fixture.stdout)
+        self.assertIs(None, tc.output_fixture.stderr)
+
+    @mock.patch('os.environ')
+    def test_enabled(self, mock_env):
+        mock_env.get.return_value = 'True'
+        tc = self.FakeTestCase("test_fake_test")
+        tc.setUp()
+        self.assertIsNot(None, tc.output_fixture.stdout)
+        self.assertIsNot(None, tc.output_fixture.stderr)
+
 
 class TestManualMock(base.BaseTestCase):
 

tests/unit/test_output.py

@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import sys
+
+from oslotest import output
+
+import mock
+import testtools
+
+
+class CaptureOutputTest(testtools.TestCase):
+
+    @mock.patch('os.environ')
+    def test_disabled(self, mock_env):
+        mock_env.get.return_value = ''
+        f = output.CaptureOutput()
+        f.setUp()
+        self.assertIs(None, f.stdout)
+        self.assertIs(None, f.stderr)
+        self.assertIsNot(sys.stdout, f.stdout)
+        self.assertIsNot(sys.stderr, f.stderr)
+
+    @mock.patch('os.environ')
+    def test_enabled(self, mock_env):
+        mock_env.get.return_value = 'True'
+        f = output.CaptureOutput()
+        f.setUp()
+        self.assertIsNot(None, f.stdout)
+        self.assertIsNot(None, f.stderr)
+        self.assertIs(sys.stdout, f.stdout)
+        self.assertIs(sys.stderr, f.stderr)