def METHOD_NAME(self):
    m = pe.ConcreteModel()
    m.x = pe.Var()
    m.y = pe.Var()
    e = pe.Expr_if(m.x <= 0, m.y + m.x == 0, m.y - m.x == 0)
    pn = convert_expression_to_prefix_notation(e)
    expected = [
        (Expr_ifExpression, 3),
        (InequalityExpression, 2),
        m.x,
        0,
        (EqualityExpression, 2),
        (LinearExpression, 2),
        (MonomialTermExpression, 2),
        1,
        m.y,
        (MonomialTermExpression, 2),
        1,
        m.x,
        0,
        (EqualityExpression, 2),
        (LinearExpression, 2),
        (MonomialTermExpression, 2),
        1,
        m.y,
        (MonomialTermExpression, 2),
        -1,
        m.x,
        0,
    ]
    self.assertEqual(pn, expected)