testFixersPriority: verbose assertion message

tests/AutoReview/FixerFactoryTest.php

@@ -42,7 +42,7 @@ final class FixerFactoryTest extends TestCase
      */
     public function testFixersPriority(FixerInterface $first, FixerInterface $second)
     {
-        $this->assertLessThan($first->getPriority(), $second->getPriority());
+        $this->assertLessThan($first->getPriority(), $second->getPriority(), sprintf('"%s" should have less priority than "%s"', get_class($second), get_class($first)));
     }
 
     public function provideFixersPriorityCases()