In a world where this needs to be solved with TDD there are a few approaches.
If you were pair programming, your pair could always create a new failing test with the current implementation.
Realistically I would want tests for the interesting cases like zero, positive even, negative even, and the odds.
Another approach would be property based testing. One could create sequence generators that randomly generate even or odd numbers and tests the function with those known sequences. I don’t typically use this approach, but it would be a good fit here.
Really in pair programming, your pair would get sick of your crap if you were writing code like this, remind you of all the work you need to get done this week, and you’d end up using modulus and move on quickly.
If you were pair programming, your pair could always create a new failing test with the current implementation.
But I’m not pair programming. And you can’t always create a new failing test because int is a finite type. There are only about 4 billion cases to handle.
Which might take a while to type up manually, but that’s why we have meta-programming: Code that generates code. (In C++ you could even use templates, but you might run into compiler recursion limits.)
More to the point, the risk with TDD is that all development is driven by failing test cases, so a naive approach will end up “overfitting”, producing exactly the code required to make a particular set of tests pass and nothing more. “It can’t pass all test cases”? It doesn’t have to. For TDD, it only needs to pass the tests that have actually been written. You can’t test all combinations of all inputs.
(Also, if you changed this function to use modulus, it would handle more cases than before, which is a change in behavior. You’re not supposed to do that when refactoring; refactoring should preserve semantics.)
In a world where this needs to be solved with TDD there are a few approaches.
If you were pair programming, your pair could always create a new failing test with the current implementation.
Realistically I would want tests for the interesting cases like zero, positive even, negative even, and the odds.
Another approach would be property based testing. One could create sequence generators that randomly generate even or odd numbers and tests the function with those known sequences. I don’t typically use this approach, but it would be a good fit here.
Really in pair programming, your pair would get sick of your crap if you were writing code like this, remind you of all the work you need to get done this week, and you’d end up using modulus and move on quickly.
But I’m not pair programming. And you can’t always create a new failing test because
intis a finite type. There are only about 4 billion cases to handle.Which might take a while to type up manually, but that’s why we have meta-programming: Code that generates code. (In C++ you could even use templates, but you might run into compiler recursion limits.)
More to the point, the risk with TDD is that all development is driven by failing test cases, so a naive approach will end up “overfitting”, producing exactly the code required to make a particular set of tests pass and nothing more. “It can’t pass all test cases”? It doesn’t have to. For TDD, it only needs to pass the tests that have actually been written. You can’t test all combinations of all inputs.
(Also, if you changed this function to use modulus, it would handle more cases than before, which is a change in behavior. You’re not supposed to do that when refactoring; refactoring should preserve semantics.)
Read the article about property based testing. It is the middle ground between what you are describing and practicality.
I often pair with myself, which sounds silly but you can write failing tests by yourself, it just isn’t as fun.
But where’s the fun in that?
There are so many better
for obfuscationways of checking for oddness!(a & 1) > 0 a.toString()[a.toString().length()-1] - '1' == 0 iseven(a)?(1==0):(1!=0)