The Mosquitto test suite can be invoked using either of
make test
make check
The tests run in series and due to the nature of some of the tests being made can take a while.
To run the tests with some parallelism, use
make ptest
This runs up to 20 tests in parallel at once, yielding much faster overall run time at the expense of having up to 20 instances of Python running at once. This is not a particularly CPU intensive option, but does require more memory and may be unsuitable on e.g. a Raspberry Pi.
The tests require Python 3 and CUnit to be installed.