How can one reliably run unittests

[jfondren]

On Thursday, 26 August 2021 at 23:29:20 UTC, Dennis wrote:
> On Thursday, 26 August 2021 at 09:38:54 UTC, deadalnix wrote:
>> But having main declared twice is some special level of 
>> nonsense. In what case could I possibly want two main?
>
> When there's both a main function and the `-main` flag, should 
> `-main` do nothing or override the main function with an empty 
> one?

In the -unittest usage, and without some code overriding the 
runtime's testrunner, these are equivalent outcomes since dmd no 
longer runs main after unittests:

```d
import std.stdio;
unittest { writeln("unittest"); }
void main() { writeln("main"); }
```

contrast:

```
$ dmd -unittest -run ignoremain.d
unittest
1 modules passed unittests

$ gdc -funittest -o not-ignored ignoremain.d
$ ./not-ignored
unittest
main
```