Catch block not hit in unittest

[Lucia Cojocaru via Digitalmars-d-learn]

On Thursday, 24 November 2016 at 14:47:32 UTC, Jonathan M Davis 
wrote:
> On Thursday, November 24, 2016 13:42:25 Kagamin via 
> Digitalmars-d-learn wrote:
>> Linux? Probably another bug.
>> Try this:
>> unittest
>> {
>>      import core.exception : UnicodeException;
>>      void f()
>>      {
>>          string ret;
>>          int i = -1;
>>          ret ~= i;
>>      }
>>
>>      try
>>      {
>>          f();
>>      }
>>      catch(UnicodeException e)
>>      {
>>          assert(e.msg == "Invalid UTF-8 sequence");
>>      }
>> }
>
> If you're doing that, you might as well use 
> std.exception.assertThrown or collectException. e.g.
>
> assertThrown!UnicodeException(f());
>
> or
>
> assert(collectException!UnicodeException(f()).msg ==
>        "Invalid UTF-8 sequence.");
>
> You could also do the same with a lambda to avoid the explicit 
> function.
>
> Regardless, I don't know why the OP is hitting this problem, 
> and unfortunately, I can't test it on my local machine at the 
> moment to try and see what's going on.
>
> - Jonathan M Davis

Thanks Kagamin and Jonathan for your suggestions!

I was able to hack my way around it. In druntime there are other 
modules which need the exact same thing and have their own 
assertThrown template:
https://github.com/dlang/druntime/search?utf8=%E2%9C%93&q=assertThrown

So I did the same thing and defined assertThrown in my unittest. 
Now it works fine:
unittest
{
     import core.exception : UnicodeException;

     static void assertThrown(T : Throwable = Exception, E)(lazy E 
expr, string msg)
     {
         try
             expr;
         catch (T e) {
             assert(e.msg == msg);
             return;
         }
     }

     static void f()
     {
         string ret;
         int i = -1;
         ret ~= i;
     }

     assertThrown!UnicodeException(f(), "Invalid UTF-8 sequence");
}

It is still unclear why this approach is necessary.

Thanks,
Lucia