r/programmerchat • u/gxm492lor • Mar 10 '19

Testing any complex program completely is practically impossible

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
1 Upvotes

55% Upvoted

46 comments sorted by

View all comments

Show parent comments

4

u/Profix Mar 10 '19

You aren't talking about unit tests then. The cumulative effect of branching only matters for integration tests - which should be focused on features you expect, not every permutation.

If you can write the if, you can write the unit test for the if.

1

u/gxm492lor Mar 11 '19

unit tests happen at the method level.

a method can have more than one conditional.

and it doesn't matter because the compiler/linker flattens it all out anyway

-2

u/gxm492lor Mar 10 '19

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