Add test

Author: VincentLanglet

tests/PHPStan/Analyser/nsrt/bug-13144.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Bug13144;
+
+use ArrayObject;
+
+use function PHPStan\Testing\assertType;
+
+$arr = new ArrayObject(['a' => 1, 'b' => 2]);
+
+assertType('ArrayObject<string, int>', $arr); // correctly inferred as `ArrayObject<string, int>`
+
+$a = $arr['a']; // ok
+$b = $arr['b']; // ok
+
+assertType('int|null', $a); // correctly inferred as `int|null`
+assertType('int|null', $b); // correctly inferred as `int|null`
+
+
+['a' => $a, 'b' => $b] = $arr; // ok
+
+assertType('int|null', $a); // incorrectly inferred as `mixed`
+assertType('int|null', $b); // incorrectly inferred as `mixed`