Make tests portable

Author: sebastianbergmann

tests/tests/Report/CoberturaTest.php

@@ -13,6 +13,7 @@
 use function libxml_clear_errors;
 use function libxml_get_errors;
 use function libxml_use_internal_errors;
+use function realpath;
 use function sprintf;
 use function str_replace;
 use function trim;
@@ -85,7 +86,7 @@ private function assertAndValidate(string $expectationFile, string $coberturaXml
 
         $coberturaXml = str_replace(
             '<?xml version="1.0" encoding="UTF-8"?>',
-            '<?xml version="1.0" encoding="UTF-8"?>' . "\n" . '<!DOCTYPE coverage SYSTEM "' . __DIR__ . '/../../_files/Report/Cobertura/coverage-04.dtd">',
+            '<?xml version="1.0" encoding="UTF-8"?>' . "\n" . '<!DOCTYPE coverage SYSTEM "' . realpath(__DIR__ . '/../../_files/Report/Cobertura/coverage-04.dtd') . '">',
             $coberturaXml,
         );