update testing to account for new stuff

.travis.yml

@@ -1,13 +1,15 @@
 language: python
+env:
+    - MPLBACKEND='agg'
 python:
     - '2.7'
     - '3.4'
     - '3.5'
     - '3.6'
 install:
-    - pip install .
-    - pip install -r requirements.txt
-    - pip install shapely coveralls
+    - pip install . # intsall package
+    - pip install -r requirements.txt # install requires
+    - pip install shapely coveralls matplotlib # only for testing
 script:
     - nosetests --verbose --with-coverage --cover-package=cartoframes
 after_success:

test/test_context.py

@@ -218,15 +218,22 @@ def test_cartoframes_query(self):
     def test_cartocontext_map(self):
         """CartoContext.map"""
         from cartoframes import Layer, QueryLayer, BaseMap
+        import matplotlib
+        matplotlib.use('agg')
+        import matplotlib.pyplot as plt
         import IPython
         cc = cartoframes.CartoContext(base_url=self.baseurl,
                                       api_key=self.apikey)
 
         # test with no layers - should produce basemap
+        basemap_only_static_mpl = cc.map(interactive=False)
+        cartoframes.context.HAS_MATPLOTLIB = False
         basemap_only_static = cc.map(interactive=False)
         basemap_only_interactive = cc.map(interactive=True)
 
-        # are of instance of IPython HTML class
+        # are of the correct type instances
+        self.assertIsInstance(basemap_only_static_mpl,
+                              plt.Axes)
         self.assertIsInstance(basemap_only_static,
                               IPython.core.display.HTML)
         self.assertIsInstance(basemap_only_interactive,