public void DerivativeTest1()
{
IExpression exp = new Sec(new Mul(new Number(2), new Variable("x")));
IExpression deriv = exp.Differentiate();
Assert.AreEqual("(2 * 1) * (tan(2 * x) * sec(2 * x))", deriv.ToString());
}
public void DerivativeTest2()
{
// sec(2x)
Number num = new Number(2);
Variable x = new Variable("x");
Mul mul = new Mul(num, x);
IExpression exp = new Sec(mul);
IExpression deriv = exp.Differentiate();
Assert.AreEqual("(2 * 1) * (tan(2 * x) * sec(2 * x))", deriv.ToString());
num.Value = 4;
Assert.AreEqual("sec(4 * x)", exp.ToString());
Assert.AreEqual("(2 * 1) * (tan(2 * x) * sec(2 * x))", deriv.ToString());
}