by Andy Masters
25. March 2011 16:06
I was playing around with TDD again. It highlighted to me just how bad a very simple and correct looking function can be.
In maths, Factorial(n) is written n!, so Factorial(10) is the same as 10!.
1! =1
2! =1*2=2
3! =1*2*3=6
n! = n * n-1 * n-2 * ... * 1
I wrote this function without TDD to calculate the nth Factorial number recursively:
public static long FactorialRecursive(int index)
{
if (index==1)
{
return 1;
}
return index * FactorialRecursive(--index);
}
I then rewrote the function using TDD. I discovered 4 quite serious bugs in the above code, see if you can find them (answers in my next post, although I expect there will be others that I've missed too). I also tried a radically different approach to writing the function, how would you write it?
The benefit of unit-testing is that seemingly correct code should get smoked out.
The benefit of TDD is you get a better design, and just enough tests to prove it is correct.
Subscribe