Added some tests for batch_fetch

tests/test_batch_fetch.py

@@ -0,0 +1,34 @@
+from pytest import raises
+from sqlalchemy_utils import batch_fetch
+from tests import TestCase
+
+
+class TestBatchFetch(TestCase):
+    def setup_method(self, method):
+        TestCase.setup_method(self, method)
+        category = self.Category(name=u'Category #1')
+        category.articles = [
+            self.Article(name=u'Article 1'),
+            self.Article(name=u'Article 2')
+        ]
+        category2 = self.Category(name=u'Category #2')
+        category2.articles = [
+            self.Article(name=u'Article 3'),
+            self.Article(name=u'Article 4'),
+            self.Article(name=u'Article 5')
+        ]
+        self.session.add(category)
+        self.session.add(category2)
+        self.session.commit()
+
+    def test_raises_error_if_relationship_not_found(self):
+        categories = self.session.query(self.Category).all()
+        with raises(AttributeError):
+            batch_fetch(categories, 'unknown_relation')
+
+    def test_supports_relationship_attributes(self):
+        categories = self.session.query(self.Category).all()
+        batch_fetch(categories, self.Category.articles)
+        query_count = self.connection.query_count
+        categories[0].articles  # no lazy load should occur
+        assert self.connection.query_count == query_count