Adding trait for GeneratorAwareExtension (#165)

* Adding trait for GeneratorAwareExtension

* Fixes

* Fix: Remove unnecessary initialization

* Fix: Add test

Co-authored-by: Andreas Möller <am@localheinz.com>

src/Faker/Extension/GeneratorAwareExtensionTrait.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Faker\Extension;
+
+use Faker\Generator;
+
+/**
+ * A helper trait to be used with GeneratorAwareExtension.
+ */
+trait GeneratorAwareExtensionTrait
+{
+    /**
+     * @var Generator|null
+     */
+    private $generator;
+
+    /**
+     * @return static
+     */
+    public function withGenerator(Generator $generator): self
+    {
+        $instance = clone $this;
+
+        $instance->generator = $generator;
+
+        return $instance;
+    }
+}

test/Faker/Extension/GeneratorAwareExtensionTest.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Faker\Test\Extension;
+
+use Faker\Extension\Extension;
+use Faker\Extension\GeneratorAwareExtensionTrait;
+use Faker\Generator;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \Faker\Extension\GeneratorAwareExtensionTrait
+ */
+final class GeneratorAwareExtensionTest extends TestCase
+{
+    public function testWithGeneratorClonesExtensionAndSetsGenerator(): void
+    {
+        $generator = new Generator();
+
+        $extension = new class() implements Extension {
+            use GeneratorAwareExtensionTrait;
+
+            public function generator(): Generator
+            {
+                return $this->generator;
+            }
+        };
+
+        $mutated = $extension->withGenerator($generator);
+
+        self::assertNotSame($mutated, $extension);
+        self::assertSame($generator, $mutated->generator());
+    }
+}