> I would love to used PBT more, but many tests I write have only one answer per input. Think sum like aggregations. Not quite sure what you mean by "only one

> I would love to used PBT more, but many tests I write have only one answer per input. Think sum like aggregations. Not quite sure what you mean by "only one answer per input" (that it's a function, i.e. a 1:1 mapping?), but there are of lots of properties that aggregations might typically need to satisfy, e.g. off the top of my head: # Identity element forAll(pre, post) { assertEqual( agg(pre ++ [agg([])] ++ post), agg(pre ++ post) ) } # Invariant to order forAll(elems, seed) { assertEqual( agg(elems), agg(permute(elems, seed)) ) } # Left-associative forAll(xs, ys, zs) { assertEqual( agg([agg(xs ++ ys)] ++ zs), agg(xs ++ ys ++ zs) ) } # Right-associative forAll(xs, ys, zs) { assertEqual( agg(xs ++ [agg(yz ++ zs)]), agg(xs ++ ys ++ zs) ) } (FYI these typical properties of a (commutative) monoid, which is an algebraic structure that describes many "aggregation-like" operations)