unittest behaviour

[user1234]

On Sunday, 15 December 2024 at 08:45:22 UTC, DLearner wrote:
> Please consider:
>
> ```
> size_t foo() {
>    static size_t var1 = 1;
>
>    var1 = var1 + 1;
>    return var1;
> }
>
> unittest {
>
>    assert(foo() == 2);
>    assert(foo() == 3);
> }
>
> ```
>
> which works as expected.
>
> But
>
> ```
> size_t foo1() {
>    static size_t var1 = 1;
>
>    var1 = var1 + 1;
>    return var1;
> }
>
> unittest {
>    assert(foo1() == 2);
> }
>
> unittest {
>    assert(foo1() == 2);
> }
>
> ```
>
> Fails on the second unittest.
>
> I appreciate this behaviour matches the docs (so not a bug), 
> but is it desirable?

Yes. Remember that you have the function attribute `pure` [[1]]. 
It would have avoided the problem.. for instance:

```d
size_t foo1() {
    static size_t var1 = 1;

    var1 = var1 + 1;
    return var1;
}

pure unittest {
    assert(foo1() == 2);
}

pure unittest {
    assert(foo1() == 2);
}
```
refuses to compile with the following errors

> test.d(9,15): Error: `pure` function 
> `temp_7F58D0140210.__unittest_L8_C6` cannot call impure 
> function `temp_7F58D0140210.foo1`
> test.d(13,15): Error: `pure` function 
> `temp_7F58D0140210.__unittest_L12_C6` cannot call impure 
> function `temp_7F58D0140210.foo1`

With `pure` that you would have seen the problem, that is "oh, 
the global state".

[1]: https://dlang.org/spec/function.html#pure-functions