Merge pull request matplotlib#2379 from mdboom/better-message-about-missing-test-data

Make matplotlib.test() print meaninful messages when baseline images are not installed

Author: pelson

lib/matplotlib/tests/__init__.py

@@ -2,13 +2,24 @@
 from matplotlib import rcParams, rcdefaults, use
 
 import difflib
+import os
 
 from matplotlib import rcParams, rcdefaults, use
 
 
 _multiprocess_can_split_ = True
 
 
+# Check that the test directories exist
+if not os.path.exists(os.path.join(
+        os.path.dirname(__file__), 'baseline_images')):
+    raise IOError(
+        'The baseline image directory does not exist. '
+        'This is most likely because the test data is not installed. '
+        'You may need to install matplotlib from source to get the '
+        'test data.')
+
+
 def setup():
     # The baseline images are created in this locale, so we should use
     # it during all of the tests.