Improve assertion error messages in ConstructTest.php

Author: rodrigoprimo

tests/Core/Files/FileList/ConstructTest.php

@@ -82,8 +82,16 @@ public function testConstruct($files, $expectedFiles)
         ksort($fileListArray);
 
         foreach ($fileListArray as $filePath => $fileObject) {
-            $this->assertSame($expectedFiles[$i], $filePath, 'File path mismatch at index '.$i);
-            $this->assertInstanceOf('PHP_CodeSniffer\Files\File', $fileObject, 'File object mismatch at index '.$i);
+            $this->assertSame(
+                $expectedFiles[$i],
+                $filePath,
+                sprintf('File path mismatch: expected "%s", got "%s"', $expectedFiles[$i], $filePath)
+            );
+            $this->assertInstanceOf(
+                'PHP_CodeSniffer\Files\File',
+                $fileObject,
+                sprintf('File object for "%s" is not an instance of PHP_CodeSniffer\Files\File', $filePath)
+            );
             $i++;
         }