human
I wrote the below code

    if (not trial_args):
        trial_args = ['--rterrors', 'flocker.acceptance']
    def check_result(f):
        f.trap(ProcessTerminated)
        if (f.value.exitCode is not None):
            return f.value.exitCode
        else:
            return f
    return run(reactor, (['trial'] + list(trial_args)), env=extend_environ(**get_trial_environment(cluster, package_source))).addCallbacks(callback=(lambda _: 0), errback=check_result)

What's a good function header?
 Here's a good function header?
assistant
#Here's a good function header.

def run_tests(reactor, cluster, trial_args, package_source):