Fixed test when pydot is not available

theano/tests/test_printing.py

 """
 Tests of printing functionality
 """
+
+
 import logging
 import StringIO
 
+from nose.plugins.skip import SkipTest
+
 import theano
 import theano.tensor as tensor
 
@@ -17,6 +21,12 @@ def test_pydotprint_cond_highlight():
     I did them to help debug stuff.
     """
 
+    # Skip test if pydot is not available.
+    try:
+        import pydot
+    except ImportError:
+        raise SkipTest('pydot not available')
+
     x = tensor.dvector()
     f = theano.function([x], x*2)
     f([1,2,3,4])