Unit testing a function returning void

[Imperatorn]

On Thursday, 3 November 2022 at 10:26:04 UTC, Imperatorn wrote:
> On Thursday, 3 November 2022 at 10:00:27 UTC, Bruno Pagis wrote:
>> Good morning,
>> I have the following class:
>>
>> ```
>> class A {
>>   int[] array;
>>
>>   ...
>>
>>   void print() {
>>     writeln("array = ", this.array);
>>   }
>> }
>> ```
>>
>> I would like to unit test the print function (yes, I know, not 
>> very useful on the above example since print is merely a 
>> duplicate of writeln...). Is there a way to use assert to test 
>> the output of the print function to stdout? Something like:
>> ```
>> A myClass= new A;
>> myClass.array = [1,2];
>> assert(myClass.print() == "array = [1,2]"); // I know that 
>> print does not return anything so this is wrong, but you get 
>> the idea :-)
>> ```
>> Thanks.
>
> Just so we understand, do you want to verify that the output is 
> indeed directed to stdout and not some other stream?

Just for documentation purposes, if you wished to redirect I 
believe you could do something like this (untested):

```d
auto original = stdout; // save
stdout.open(newdest, "wt"); // redirect

// do stuff, check newdest

stdout = original; // restore
```