if (classOutput.size(ReadFileSystem.FILE) > 0) {
File root = File.createTempFile("juzu", "");
Assert.assertTrue(root.delete());
Assert.assertTrue(root.mkdirs());
root.deleteOnExit();
ReadWriteFileSystem classes = new DiskFileSystem(root);
classOutput.copy(new Filter.Default<O>() {
@Override
public boolean acceptFile(O file, String name) throws IOException {
return name.endsWith(".class");
}