Add WebTest global fixture for tests

From https://gist.github.com/magopian/6673250

conftest.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+import pytest
+from django_webtest import DjangoTestApp, WebTestMixin
+
+
+@pytest.fixture(scope='function')
+def app(request):
+    """WebTest's TestApp.
+
+    Patch and unpatch settings before and after each test.
+
+    WebTestMixin, when used in a unittest.TestCase, automatically calls
+    _patch_settings() and _unpatchsettings.
+
+    source: https://gist.github.com/magopian/6673250
+    """
+    wtm = WebTestMixin()
+    wtm._patch_settings()
+    request.addfinalizer(wtm._unpatch_settings)
+    return DjangoTestApp()