dot-dsl: Fix error and implement exception message checks (#1168)
dot-dsl: Fix error and implement exception message checks (#1168)

* dot-dsl: Fix error in tests

* dot-dsl: Implement checks for exception messages

exercism/xpython,jmluy/xpython,behrtam/xpython,smalley/python,exercism/xpython,jmluy/xpython,exercism/python,N-Parsons/exercism-python,smalley/python,behrtam/xpython,N-Parsons/exercism-python,exercism/python