Hmm @adamcarter. I do understand the problem you want to solve. So support the idea of providing a cleaner way to test lazily computed and/or opaque types. SwiftUI views are of course a great example. One I have been struggling with to test myself as well.
But I'm unsure about the proposed solution. Mainly because if forfeits the regular
GIVEN
WHEN
THEN
sequence by taking the expectation (assertion) out of this sequence by making it part of the @Test declaration. Having a test without an #expect is very alien to me. In particular as it's a great way of spotting 'liar tests': i.e. tests that don't assert on anything and are there (most likely) just to increase the coverage percentage.
Following this train of thought, adding the assertion to the @Suite is not something I would recommend. Suites are not meant to define how something is tested right? Only to group them in a certain, logical way?
I'm sorry if these comments only criticise your proposal without proposing any alternatives for the very real issue you present. It's just, I don't have an alternative yet, but I will try and think of one and let you know if I find one.