Converted #736 test case into an integration test

While the `.phpt` test was valid, it does not produce coverage nor mutation test
output, and requires to run in a separate test: converting it back to a more typical
PHPUnit test makes it a bit quicker to run, and also puts it under `vimeo/psalm`'s
watchful eyes.

Author: Ocramius

tests/ProxyManagerTest/Functional/AccessInterceptorValueHolderFunctionalTest.php

@@ -25,6 +25,7 @@
 use ProxyManagerTestAsset\ClassWithSelfHint;
 use ProxyManagerTestAsset\EmptyClass;
 use ProxyManagerTestAsset\OtherObjectAccessClass;
+use ProxyManagerTestAsset\ReferenceIncrementDecrementClass;
 use ProxyManagerTestAsset\VoidCounter;
 use ReflectionClass;
 use ReflectionProperty;
@@ -696,6 +697,79 @@ public function testWillInterceptAndReturnEarlyOnVoidMethod(): void
         self::assertSame($increment + $addMore + 1, $object->counter);
     }
 
+    public function testByReferencePassedArgumentsAreGivenAsReferenceToInterceptorCallbacks(): void
+    {
+        $proxy = (new AccessInterceptorValueHolderFactory())->createProxy(
+            new ReferenceIncrementDecrementClass(),
+            [
+                'incrementReference' => static function (
+                    object $proxy,
+                    ReferenceIncrementDecrementClass $instance,
+                    string $method,
+                    array $args,
+                    bool &$returnEarly
+                ): void {
+                    self::assertSame(0, $args['reference']);
+
+                    $returnEarly       = true;
+                    $args['reference'] = 5;
+                },
+            ]
+        );
+
+        $number = 0;
+
+        $proxy->incrementReference($number);
+
+        self::assertSame(5, $number, 'Number was changed by interceptor');
+    }
+
+    public function testByReferenceArgumentsAreForwardedThroughInterceptorsAndSubject(): void
+    {
+        $proxy = (new AccessInterceptorValueHolderFactory())->createProxy(
+            new ReferenceIncrementDecrementClass(),
+            [
+                'incrementReference' => static function (
+                    object $proxy,
+                    ReferenceIncrementDecrementClass $instance,
+                    string $method,
+                    array $args,
+                    bool &$returnEarly
+                ): void {
+                    self::assertSame(0, $args['reference']);
+
+                    $returnEarly       = false;
+                    $args['reference'] = 5;
+                },
+            ],
+            [
+                'incrementReference' => static function (
+                    object $proxy,
+                    ReferenceIncrementDecrementClass $instance,
+                    string $method,
+                    array $args,
+                    mixed $returnValue,
+                    bool &$returnEarly
+                ): void {
+                    self::assertIsInt($args['reference']);
+
+                    $returnEarly        = false;
+                    $args['reference'] *= 2;
+                },
+            ]
+        );
+
+        $number = 0;
+
+        $proxy->incrementReference($number);
+
+        self::assertSame(
+            12,
+            $number,
+            'Number was changed by prefix interceptor, then incremented, then doubled by suffix interceptor'
+        );
+    }
+
     private static function assertByRefVariableValueSame(mixed $expected, mixed & $actual): void
     {
         self::assertSame($expected, $actual);

tests/ProxyManagerTestAsset/ReferenceIncrementDecrementClass.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ProxyManagerTestAsset;
+
+class ReferenceIncrementDecrementClass
+{
+    public function incrementReference(int & $reference): void
+    {
+        $reference += 1;
+    }
+}