map_variables: simplify tests with assertRaises

theano/scan_module/tests/test_scan_utils.py

 import sys
 import itertools
+import unittest
 import numpy
 import theano
 from theano import tensor
@@ -21,7 +22,7 @@ def test_equal_compuations():
 # map_variables #
 #################
 
-class TestMapVariables(object):
+class TestMapVariables(unittest.TestCase):
     @staticmethod
     def replacer(graph):
         return getattr(graph.tag, "replacement", graph)
@@ -104,15 +105,8 @@ class TestMapVariables(object):
 
         s, _ = theano.scan(step, sequences=x,
                            outputs_info=[numpy.array(0.)])
-        try:
-            s2, = map_variables(self.replacer, [s])
-        except NotImplementedError as e:
-            e = sys.exc_info()[1]
-            assert("introduces shared variable" in str(e))
-            return
-
-        # test failed
-        return 0
+        self.assertRaises(NotImplementedError,
+                          map_variables, self.replacer, [s])
 
     def test_scan_with_shared_update2(self):
         x = tensor.vector('x')
@@ -135,15 +129,8 @@ class TestMapVariables(object):
 
         s, _ = theano.scan(step, sequences=x,
                            outputs_info=[numpy.array(0.)])
-        try:
-            s2, = map_variables(self.replacer, [s])
-        except NotImplementedError as e:
-            e = sys.exc_info()[1]
-            assert("introduces shared variable" in str(e))
-            return
-
-        # test failed
-        return 0
+        self.assertRaises(NotImplementedError,
+                          map_variables, self.replacer, [s])
 
     def test_leaf_inside_scan(self):
         x = tensor.vector('x')