My solution so far:

python ./odoo.py -i module_to_test --log-level=test -d minimal_database --test-enable --stop-after-init

This is pretty common advice

However, the solution seems to be not to use the --test-file parameter, since this unexpectedly runs all tests of all dependent modules and does whatever else, making it too long to execute.

Another part of the solution is to use a minimal database where just the module to be tested plus its dependencies of course is installed.

Now the above command takes only several seconds to execute at my machine even if the tested code uses objects from dependent modules. If only I could prevent the module to make an update each time while running the tests in order to make it even faster and more efficient ...