public void Variables(double x, double y)
        {
            Terminal    op1 = new Terminal("x0");
            Terminal    op2 = new Terminal("x1");
            Mult        m   = new Mult(op1, op2);
            Div         d   = new Div(op1, op2);
            Addition    a   = new Addition(op1, op2);
            Subtraction s   = new Subtraction(op1, op2);

            Assert.True(m.Compute(x, y) == x * y);
            Assert.True(d.Compute(x, y) == x / y);
            Assert.True(a.Compute(x, y) == x + y);
            Assert.True(s.Compute(x, y) == x - y);
        }
        public void Constants(string x1, string x2, double r1, double r2)
        {
            Terminal    op1 = new Terminal(x1);
            Terminal    op2 = new Terminal(x2);
            Mult        m   = new Mult(op1, op2);
            Div         d   = new Div(op1, op2);
            Addition    a   = new Addition(op1, op2);
            Subtraction s   = new Subtraction(op1, op2);

            Assert.True(m.Compute(0) == r1 * r2);
            Assert.True(a.Compute(0) == r1 + r2);
            Assert.True(s.Compute(0) == r1 - r2);
            Assert.True(d.Compute(0) == r1 / r2);
        }