This would eliminate the need to add an Attribute Creator after every port if I want to use these test results for things further in the process like "Groupby" Functions etc.
This is an interesting idea for sure. I can see this being an interesting way of solving a long standing request as well. But
@erik_jan is right that you can do a similar thing via Conditional setting. But still we'll consider this...
This would also be very useful after the change detector transformer instead of a separate attribute creator on each port. Attribute name to be set by the user, with values of unchanged, deleted and added ?
I agree that this would be helpful and is a sensible addition. As the TestFilter ports are not attributes, I do not see how to integrate the ports into the data flow with an AttributeCreator, even using Conditional Values? I checked attributes that were not exposed by default and couldn't find the ports there.
I completely understand that the AttributeCreator is able to generate similar results as I have a few workspaces with that exact functionality and it is often better if you need to generate multiple attributes based on a test.
That said, if they're processed differently based on the test/attribute I would generally be filtering straight after the AttributeCreator so this functionality could easily reduce the number of transformers required.
I see this as being similar to the '_predicate' attribute option from a SpatialFilter. You don't need to take the value but still available.