Allow running test suite with osx tar, fixes #5662

tests/Composer/Test/Downloader/XzDownloaderTest.php

@@ -72,7 +72,7 @@ class XzDownloaderTest extends TestCase
             $downloader->download($packageMock, $this->getUniqueTmpDirectory());
             $this->fail('Download of invalid tarball should throw an exception');
         } catch (\RuntimeException $e) {
-            $this->assertContains('File format not recognized', $e->getMessage());
+            $this->assertRegexp('/(File format not recognized|Unrecognized archive format)/i', $e->getMessage());
         }
     }
 }