More descriptive error when accessing an unhandled mobject attribute (#1059)

* More descriptive error when accessing an unhandled mobject attribute

* Fix tests, stop taking advantage of mobject representations

Author: friedkeenan

manim/mobject/mobject.py

@@ -352,7 +352,7 @@ def setter(self, value):
             return types.MethodType(setter, self)
 
         # Unhandled attribute, therefore error
-        raise AttributeError
+        raise AttributeError(f"{type(self).__name__} object has no attribute '{attr}'")
 
     @property
     def width(self):

tests/test_get_set.py

@@ -36,5 +36,5 @@ def test_set_compat_layer():
 def test_nonexistent_attr():
     m = Mobject()
 
-    with pytest.raises(AttributeError):
+    with pytest.raises(AttributeError, match="object has no attribute"):
         m.test