@Test(expected = IllegalAttributeException.class)
public void testIsExternalInvalid3() throws Exception {

    File testFile = new File(SRGS_BASE + "external/invalid3.grxml");
    /* create a VoiceXmlDocument from the string */
    final VoiceXmlDocument document = new VoiceXmlDocument(
            new InputSource(new FileReader(testFile)));
    /* Lets test, if it is srgs+xml */
    final VoiceXmlNode node = (VoiceXmlNode) document.getFirstChild();
    if (node instanceof Grammar) {
        /* ok, it seems to be a srgs xml grammar */
        Grammar gr = (Grammar) node;
        /* now test isExternalMethod */
        gr.isExternalGrammar();
    }
}