Update Bug13813IntegrationTest.php

Author: staabm

tests/PHPStan/Analyser/Bug13813IntegrationTest.php

@@ -23,6 +23,15 @@ public function testBug13813(): void
 		]);
 		$this->assertCount(2, $analyzerResult->getAllPhpErrors());
 		$this->assertCount(2, $analyzerResult->getFilteredPhpErrors());
+
+		$this->assertSame(
+			'Warning: Undefined variable $x',
+			$analyzerResult->getAllPhpErrors()[0]->getMessage()
+		);
+		$this->assertSame(
+			'Warning: Undefined variable $x',
+			$analyzerResult->getAllPhpErrors()[1]->getMessage()
+		);
 	}
 
 	/**