Note, that I see this error on armel (buster-backports), too:
https://buildd.debian.org/status/fetch.php?pkg=libmodbus&arch=armel&ver=3.1.6-2%7Ebpo10%2B1&stamp=1582655638(from: https://buildd.debian.org/status/package.php?p=libmodbus&suite=buster-backports)
FAIL: ./unit-tests.sh ===================== Starting server Starting client unit-test-server: no process found FAIL unit-tests.sh (exit status: 255)
