Consolidate some document indexing test code into a new mixin.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_indexing/tests/mixins.py

@@ -0,0 +1,14 @@
+from __future__ import unicode_literals
+
+from ..models import Index
+
+from .literals import TEST_INDEX_LABEL
+
+
+class DocumentIndexingTestMixin(object):
+    def _create_index(self):
+        # Create empty index
+        self.index = Index.objects.create(label=TEST_INDEX_LABEL)
+
+        # Add our document type to the new index
+        self.index.document_types.add(self.document_type)