serializer.output(expectedDom, sw);
String expectedStr = sw.toString();
//get the file name in case of a failure
FitsMetadataElement item = actual.getMetadataElement("filename");
DifferenceListener myDifferenceListener = new IgnoreAttributeValuesDifferenceListener();
Diff diff = new Diff(expectedStr,actualStr);
diff.overrideDifferenceListener(myDifferenceListener);
assertXMLEqual("Error comparing: "+item.getValue(),diff,true);
}