Add missing test.assert_raises() API.

Author: tshead

features/steps/cartesian-coordinates.py

@@ -7,6 +7,7 @@
 import numpy
 import toyplot.data
 
+import test
 import testing
 
 

features/steps/test.py

@@ -34,6 +34,9 @@ def assert_logs(logger=None, level=None):
 def assert_no_logs(logger=None, level=None):
     return unittest.TestCase().assertNoLogs(logger, level)
 
+def assert_raises(exception):
+    return unittest.TestCase().assertRaises(exception)
+
 def assert_sequence_equal(first, second, msg=None, seq_type=None):
     return unittest.TestCase().assertSequenceEqual(first, second, msg, seq_type)