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Yegor Bugayenko
23 May 2017

Any Program Has an Unlimited Number of Bugs

This may sound strange, but I will prove it: no matter how big or stable a piece of software is, it has an unlimited number of bugs not yet found. No matter how many of them we have already managed to find and fix, there are still too many left to count.

Let's take this simple Java method that calculates a sum of two integers as an example:

int sum(int a, int b) {
  return a + b;

This simple program has an unlimited number of bugs.

To prove this claim we just need to put two thoughts together:

It is obvious that there are at least two variables in this equation that are ambiguous: user expectations and maintainability. We can't be precise about them and that's why the number of bugs they will produce has no limit.

Of course, only a very limited subset of the entire set of bugs has any real business impact. Most of the bugs that exist in a program may stay there even after it is shipped to its users—nobody will ever find them or else the damage they cause to the user experience will be insignificant.

Finally, take a look at the method sum() one more time. How about these bugs:

I'm sure you can find many more.

BTW, Glenford J. Myers said something very similar in his book "The Art of Software Testing," which I reviewed earlier.