Provide simple PHPUnit constraint

README.md

@@ -254,6 +254,35 @@ This will test `my_function` using the `Generator::strings()` generator.
 You can also register your own Generators using the
 `Annotation::register($type, $generator)` method.
 
+## PHPUnit
+
+To use php-quickcheck with PHPUnit, the assertion `\QCheck\PHPUnit\Constraint\Prop` is provided.
+It provides a static constructor method `Prop::check`. Similar to `Quick::check`, the method takes the size and allows also passing options if needed.
+
+```php
+public function testStringsAreLessThanTenChars()
+{
+    $property = Gen::forAll([Gen::strings()], function ($s): bool {
+        return 10 > strlen($s);
+    });
+    $this->assertThat($property, Prop::check(50)); // will fail
+}
+```
+The assertion will delegate to `Quick::check($size, $property)`, and if the function returns anything but `true`, it will display a formatted failure description.
+
+```
+Failed asserting that property is true.
+Tests runs: 16, failing size: 15, seed: 1578486446175, smallest shrunk value(s):
+array (
+  0 => <failed shrunk value>,
+)
+```
+
+If an exception is thrown or a PHPUnit assertion fails, the message will be included in the output.
+
+To reproduce a test result the displayed seed can be passed via `Prop::check($size, ['seed' => 1578486446175])`.
+
+
 ## Project Status
 
 PhpQuickCheck is highly experimental and in its very early stages. Only

src/QCheck/PHPUnit/Constraint/Prop.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace QCheck\PHPUnit\Constraint;
+
+use PHPUnit\Framework\Constraint\Constraint;
+use QCheck\Quick;
+
+class Prop extends Constraint
+{
+    /**
+     * @var int
+     */
+    private $size;
+
+    /**
+     * @var array
+     */
+    private $opts;
+
+    public function __construct(int $n, array $opts = [])
+    {
+        $this->size = $n;
+        $this->opts = $opts;
+    }
+
+    public static function check($n = 100, array $opts = [])
+    {
+        return new self($n, $opts);
+    }
+
+    public function evaluate($prop, string $description = '', bool $returnResult = false)
+    {
+        $result = Quick::check($this->size, $prop, $this->opts);
+        return parent::evaluate($result, $description, $returnResult);
+    }
+
+    protected function matches($other): bool
+    {
+        return @$other['result'] === true;
+    }
+
+    public function toString(): string
+    {
+        return 'property is true';
+    }
+
+    protected function failureDescription($other): string
+    {
+        return $this->toString();
+    }
+
+    protected function additionalFailureDescription($other): string
+    {
+        return sprintf(
+            "%sTests runs: %d, failing size: %d, seed: %s, smallest shrunk value(s):\n%s",
+            $this->extractExceptionMessage($other['result']),
+            $other['num_tests'],
+            $other['failing_size'],
+            $other['seed'],
+            var_export($other['shrunk']['smallest'], true)
+        );
+    }
+
+    private function extractExceptionMessage($result): string
+    {
+        return $result instanceof \Exception ? $result->getMessage() . "\n" : '';
+    }
+
+}