Added unittest for dataframe source.

tests/test_sources.py

@@ -0,0 +1,13 @@
+import zipline.utils.factory as factory
+
+def test_dataframe_source():
+    source, df = factory.create_test_df_source()
+
+    for expected_dt, expected_price in df.iterrows():
+        sid0 = source.next()
+        sid1 = source.next()
+
+        assert expected_dt == sid0.dt == sid1.dt
+        assert expected_price[0] == sid0.price
+        assert expected_price[1] == sid1.price
+