Fix broken config UTs

https://github.com/matrix-org/synapse/pull/2755 broke log-config generation,
which in turn broke the unit tests.

tests/config/test_generate.py

@@ -12,9 +12,12 @@
 # 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.path
+import re
 import shutil
 import tempfile
+
 from synapse.config.homeserver import HomeServerConfig
 from tests import unittest
 
@@ -23,7 +26,6 @@ class ConfigGenerationTestCase(unittest.TestCase):
 
     def setUp(self):
         self.dir = tempfile.mkdtemp()
-        print self.dir
         self.file = os.path.join(self.dir, "homeserver.yaml")
 
     def tearDown(self):
@@ -48,3 +50,16 @@ class ConfigGenerationTestCase(unittest.TestCase):
             ]),
             set(os.listdir(self.dir))
         )
+
+        self.assert_log_filename_is(
+            os.path.join(self.dir, "lemurs.win.log.config"),
+            os.path.join(os.getcwd(), "homeserver.log"),
+        )
+
+    def assert_log_filename_is(self, log_config_file, expected):
+        with open(log_config_file) as f:
+            config = f.read()
+            # find the 'filename' line
+            matches = re.findall("^\s*filename:\s*(.*)$", config, re.M)
+            self.assertEqual(1, len(matches))
+            self.assertEqual(matches[0], expected)