[nwellnhof]

Technically, it doesn't has to. You can put your whole test suite into a single executable, making it run extremely fast for C/C++ projects where process startup is often much slower than running a single test unit. This approach is used in some OSS projects I've worked on but it also has its downsides.

[fuzzy2]

Some tests (e.g. unit tests) can run like this, yes. Other tests, including some benchmarks, are not meaningful when wrapped in a single process. Invocation speed and specifics matter.