fix and test image renderer

rest_pandas/renderers.py

@@ -11,6 +11,7 @@
     from io import StringIO
 
 import os
+from io import BytesIO
 
 
 class PandasBaseRenderer(BaseRenderer):
@@ -148,7 +149,7 @@ def get_pandas_kwargs(self, data, renderer_context):
         return {'ax': self.ax}
 
     def get_output(self):
-        data = StringIO()
+        data = BytesIO()
         self.fig.savefig(data, format=self.format)
         return data.getvalue()
 

tests/test_images.py

@@ -0,0 +1,33 @@
+from rest_framework.test import APITestCase
+from tests.testapp.models import TimeSeries
+import unittest
+
+try:
+    import matplotlib
+except ImportError:
+    matplotlib = None
+
+
+class ImageTestCase(APITestCase):
+    def setUp(self):
+        data = (
+            ('2014-01-01', 0.5),
+            ('2014-01-02', 0.4),
+            ('2014-01-03', 0.6),
+            ('2014-01-04', 0.2),
+            ('2014-01-05', 0.1),
+        )
+        for date, value in data:
+            TimeSeries.objects.create(date=date, value=value)
+
+    @unittest.skipUnless(matplotlib, "requires matplotlib")
+    def test_png(self):
+        response = self.client.get("/timeseries.png")
+        header = response.content[1:4]
+        self.assertEqual(header, b"PNG")
+
+    @unittest.skipUnless(matplotlib, "requires matplotlib")
+    def test_svg(self):
+        response = self.client.get("/timeseries.svg")
+        header = response.content[2:5]
+        self.assertEqual(header, b"xml")