Added unit test for bokeh png renderering

.travis.yml

@@ -29,7 +29,7 @@ install:
   - conda info -a
   - conda create -q -n test-environment python=$TRAVIS_PYTHON_VERSION scipy=0.18.1 numpy freetype nose bokeh=0.12.5 pandas=0.19.2 jupyter ipython=4.2.0 param pyqt=4 matplotlib=1.5.1 xarray datashader dask=0.13
   - source activate test-environment
-  - conda install -c conda-forge  -c scitools iris sip=4.18 plotly flexx
+  - conda install -c conda-forge  iris sip=4.18 plotly flexx selenium phantomjs
   - if [[ "$TRAVIS_PYTHON_VERSION" == "3.4" ]]; then
       conda install python=3.4.3;
     fi

tests/testrenderclass.py

@@ -9,7 +9,7 @@
 from nose.plugins.attrib import attr
 import numpy as np
 
-from holoviews import HoloMap, Image, ItemTable, Store, GridSpace, Table
+from holoviews import HoloMap, Image, ItemTable, Store, GridSpace, Table, Curve
 from holoviews.element.comparison import ComparisonTestCase
 from holoviews.plotting import Renderer
 
@@ -146,3 +146,10 @@ def test_get_size_tables_in_layout(self):
         plot = self.renderer.get_plot(table+table)
         w, h = self.renderer.get_size(plot)
         self.assertEqual((w, h), (680, 300))
+
+    def test_render_to_png(self):
+        curve = Curve([])
+        renderer = BokehRenderer.instance(fig='png')
+        png, info = renderer(curve)
+        self.assertIsInstance(png, bytes)
+        self.assertEqual(info['file-ext'], 'png')