The log of the build abruptly halts about a third of the way through the tests

Sounds like you might be hitting an issue (or similar to one) that I strike when I build recent perls (including 5.32.0 and all subsequent releases of 5.33.x) on my Windows 7 machine.
I've assumed it was something specific to my Windows 7 environment, but I don't know.

My issue is that the following test scripts hang:
cpan/IO-Compress/t/100generic-deflate.t
cpan/IO-Compress/t/105oneshot-deflate.t
cpan/IPC-Cmd/t/01_IPC-Cmd.t

If I run those tests outside of the test harness then there's no problem - so, there's no guarantee that running your tests outside of the harness will identify any issue. (Does your log always terminate in the same place ? ... maybe somewhere in the IO-Compress tests ?)
My solution is to simply replace those hanging test files with files of the same name that do nothing more than exit with an "ok" status.
Otherwise, I have to kill them using process explorer when they hang, as Control-C will kill the entire 'make test' process.

I think there's a good chance that choroba's suggestion to use verbosity will identify the file that's hanging, if indeed that's what's happening.
I think that scripting something that would run all of the tests outside of the harness would be a long, demanding and tedious job

Cheers,
Rob