Runs the test case.
Document doc;
DocumentType docType;
NamedNodeMap entities;
Node entityNode;
String entityValue;
doc = (Document) load("staff", true);
docType = doc.getDoctype();
assertNotNull("docTypeNotNull", docType);
entities = docType.getEntities();
assertNotNull("entitiesNotNull", entities);
entityNode = entities.getNamedItem("ent1");
assertNotNull("ent1NotNull", entityNode);
entityNode.setNodeValue("This should have no effect");
entityValue = entityNode.getNodeValue();
assertNull("nodeValueNull", entityValue);