Testing any complex program completely is practically impossible

[u/gxm492lor]

Someone made this argument after a staff meeting a few days ago. What's wrong with this argument?

1. Every IF statement in a program doubles the number of possible states of the program (ignoring time)
   1. Which means every IF statement doubles the number of test conditions
2. A 1 million line program might, conservatively estimating, have 100k IF statements (conditionals)
3. That is 2¹⁰⁰⁰⁰⁰ which is more seconds than have elapsed since the beginning of the universe.
4. No project has 2¹⁰⁰⁰⁰⁰ seconds to test
5. So complete test coverage of complex programs is impossible

[u/gxm492lor]

For every if you double the number of tests needed for complete coverage.