make exceptions repr tests Python 3.7-friendly by eval-repr round-trip

Author: silmeth

tests/snippets/exceptions.py

@@ -1,29 +1,37 @@
+def exceptions_eq(e1, e2):
+    return type(e1) is type(e2) and e1.args == e2.args
+
+def round_trip_repr(e):
+    assert exceptions_eq(e, eval(repr(e)))
+
 # KeyError
 empty_exc = KeyError()
 assert str(empty_exc) == ''
-assert repr(empty_exc) == 'KeyError()'
+round_trip_repr(empty_exc)
 assert len(empty_exc.args) == 0
 assert type(empty_exc.args) == tuple
 
 exc = KeyError('message')
 assert str(exc) == "'message'"
-assert repr(exc) == "KeyError('message',)"
+round_trip_repr(exc)
 
 exc = KeyError('message', 'another message')
 assert str(exc) == "('message', 'another message')"
-assert repr(exc) == "KeyError('message', 'another message')"
+round_trip_repr(exc)
 assert exc.args[0] == 'message'
 assert exc.args[1] == 'another message'
 
 class A:
     def __repr__(self):
-        return 'repr'
+        return 'A()'
     def __str__(self):
         return 'str'
+    def __eq__(self, other):
+        return type(other) is A
 
 exc = KeyError(A())
-assert str(exc) == 'repr'
-assert repr(exc) == 'KeyError(repr,)'
+assert str(exc) == 'A()'
+round_trip_repr(exc)
 
 # ImportError / ModuleNotFoundError
 exc = ImportError()