Hypothesis in particular has a very clever way to do test reduction. The key problem is that if your test generator is enforcing some constraint on the input,

Hypothesis in particular has a very clever way to do test reduction. The key problem is that if your test generator is enforcing some constraint on the input, it's not necessarily the case that naive pruning will preserve the constraint. Hypothesis has a fairly general way of enforcing that the generated test input continues to satisfy constraints.