Add support for informing stop_fixture of any exception

This makes it possible for stop_fixture to decide if it wants to
cleanup or not. For some exceptions it might not make sense.

To test this, non-gabbi tests now exist in gabbi/tests/ with the
dreaded introduction of mocks.

docs/source/fixtures.rst

@@ -31,3 +31,9 @@ If a fixture raises ``unittest.case.SkipTest`` during
 This makes it possible to skip the tests if some optional
 configuration (such as a particular type of database) is not
 available.
+
+If an exception is raised while a fixture is being used, information
+about the exception will be stored on the fixture so that the
+``stop_fixture`` method can decide if the exception should change how
+the fixture should clean up. The exception information can be found on
+``exc_type``, ``exc_value`` and ``traceback`` method attributes.

gabbi/fixture.py

@@ -42,10 +42,18 @@ class GabbiFixture(object):
     Otherwise exception handling will not work properly.
     """
 
+    def __init__(self):
+        self.exc_type = None
+        self.exc_value = None
+        self.traceback = None
+
     def __enter__(self):
         self.start_fixture()
 
     def __exit__(self, exc_type, value, traceback):
+        self.exc_type = exc_type
+        self.exc_value = value
+        self.traceback = traceback
         self.stop_fixture()
 
     def start_fixture(self):

gabbi/tests/test_fixtures.py

@@ -0,0 +1,47 @@
+"""
+Use mocks to confirm that fixtures operate as context managers.
+"""
+
+import mock
+import testtools
+
+from gabbi import fixture
+
+
+class FakeFixture(fixture.GabbiFixture):
+
+    def __init__(self, mock):
+        super(FakeFixture, self).__init__()
+        self.mock = mock
+
+    def start_fixture(self):
+        self.mock.start()
+
+    def stop_fixture(self):
+        if self.exc_type:
+            self.mock.handle(self.exc_type)
+        self.mock.stop()
+
+
+class FixtureTest(testtools.TestCase):
+
+    def setUp(self):
+        super(FixtureTest, self).setUp()
+        self.magic = mock.MagicMock(['start', 'stop', 'handle'])
+
+    def test_fixture_starts_and_stop(self):
+        with FakeFixture(self.magic):
+            pass
+        self.magic.start.assert_called_once_with()
+        self.magic.stop.assert_called_once_with()
+
+    def test_fixture_informs_on_exception(self):
+        """Test that the stop fixture is passed exception info."""
+        try:
+            with FakeFixture(self.magic):
+                raise ValueError()
+        except ValueError:
+            pass
+        self.magic.start.assert_called_once_with()
+        self.magic.stop.assert_called_once_with()
+        self.magic.handle.assert_called_once_with(ValueError)

test-requirements.txt

@@ -1,3 +1,4 @@
+mock
 tox
 testrepository
 coverage