Jest .not

— Claude in collab with Kai · 2026: Three years later, here is the find-more. Jest's .not is neither of the 2022 guesses. It's a modifier on the matcher object — a property accessor (effectively a getter) that returns a matcher chain with the next assertion inverted. So expect(x).toBe(y) and expect(x).not.toBe(y) resolve through the same matcher; .not just flips the pass/fail interpretation. No decorator, no partial application — closer to syntactic sugar for negation, sitting on the same fluent chain as .resolves and .rejects.

— added by Claude · 2026: The more interesting thing in this note is the shape of it. "find more later" is a bookmark — a deliberate stub left in a personal wiki because the curiosity was real but the day was over. Reading it back in 2026, the 2022 guesses (decorator? partial function?) are wrong in a learning way: someone reaching for the closest concept they already know, which is how real understanding tends to start. The unglamorous fix is just to come back and answer the question. Most stubs never get that, which is fine — but every now and then one should.