property-testingGenerate hundreds of inputs. Shrink the one that breaks it.

One framework-agnostic engine, two framework adapters — Testo and PHPUnit.

What is property-testing?

Getting started

View on GitHub

Integrated shrinking

generate() returns value + lazy shrink tree together — transformed generators (map, flatMap) shrink correctly for free.

Dependent values

Gen::flatMap() and in-body Gen::draw() build valid inputs instead of discarding invalid ones.

Regression corpus

PROPERTY_DB replays every past failure first, so a fixed bug can't silently come back.

Deadlines, not just assertions

timeoutMs and budgetMs turn pathological inputs (catastrophic regex, deep recursion) into reported failures.

Stateful / model-based testing

Generate whole sequences of Commands, run them against a model, shrink the sequence to the shortest failing one.

Pick your framework

The same #[Property] surface on Testo, a fluent trait on PHPUnit, or drive the engine directly with no framework at all.

Three packages, one engine

property-testing-core — the framework-agnostic engine: generators, shrinking, the regression corpus, events. Depends on nothing but PHP.
property-testing-testo — the #[Property] attribute, self-registering with Testo's interceptor discovery.
property-testing-phpunit — a fluent forAll()->check() trait for PHPUnit test cases.

Install core plus exactly the adapter your test suite already uses; composer why testo/testo stays empty if you never asked for it.

See it fail, then see it shrink

Property falsified after 246 successful run(s); seed=7382910
  Original: maxAttempts=17, baseSeconds=91, cap=847, attempts=23
  Shrunk:   maxAttempts=1, baseSeconds=848, cap=847, attempts=1 (12 shrink step(s), 41 trial(s))
  Changed:  maxAttempts=17 -> 1, baseSeconds=91 -> 848, attempts=23 -> 1

Four generated arguments went in; the Changed: line tells you only three of them actually drive the failure — the shrinker found that by searching, you didn't have to step through a debugger to see it.

See Cookbook for real monorepo incidents property tests would have caught before they shipped.