@Test
public void testExtendModel() {
String p = "P";
m = m.extend(new Symbol(p), true);
Assert.assertEquals(Boolean.TRUE, m.getStatus(new Symbol("P")));
}
@Test
public void testEmptyModel() {
Assert.assertEquals(null, m.getStatus(new Symbol("P")));
Assert.assertEquals(true, m.isUnknown(new Symbol("P")));
}