On Windows we ship 7za.exe in our binaries.
On MacOS we do the same, but the executable needs to be called with the full path.
On Linux we don't ship anything but assume it to be available from the distribution.
This is an intermediate step to have smaller unit tests. It is a trade off
between having many many test executables compared to a few bigger ones. But
this comes a lot closer to what QtTest is meant to be used.
