@Test
public void testAddWithChildren() {

    DummyExpr a = new DummyExpr("a");
    DummyExpr b = new DummyExpr("b");
    DummyExpr c = new DummyExpr("c", a, b);
    mExprModel.register(c);
    DummyExpr a2 = new DummyExpr("a");
    DummyExpr b2 = new DummyExpr("b");
    DummyExpr c2 = new DummyExpr("c", a, b);
    assertEquals(c, mExprModel.register(c2));
}