The helper function sun.tests.helpers.IOHelpers.deleteDirectory(String dir) is to delete a directory recursively. The code is as below:

=====Begin of the Code=====
static public boolean deleteDirectory(String dir) throws IOException {
        File path = new File(dir);
      // System.err.println("Deleting "+path+" "+path.isDirectory());
        if (path.exists() && path.isDirectory()) {
            File[] files = path.listFiles();
            for (int i = 0; i < files.length; i++) {
                boolean res = false;
                if (files[i].isDirectory()) {
                    res = deleteDirectory(files[i].getCanonicalPath());
                } else {
                    files[i].delete();
                }
                if (!res) {
                    System.err.println(" Could not delete " +
                            files[i].getCanonicalPath());
                }
            }
        }
        return (path.delete());
    }
=====End of the Code=====

Inside the for loop, line
files[i].delete();
should be changed to
res = files[i].delete();

And we should retrun immediately in the if block
 if (!res) {
                    System.err.println(" Could not delete " +
                            files[i].getCanonicalPath());
 }

Because it does not maks sense for us to continue to try to delete the parent directory when we already failed to delete some child file/directory.