nose-picker

nose-picker is a plugin that picks a subset of your unit tests (in django too!)

This plugin modifies nose's unit test discovery to only pick a (1/N) subset of unit tests to run. By passing in the --total-processes arguments, you pick the denominator (the N above) which you want to run. The --which-process argument controls which part of that subset to run, so if you had 5 subsets you could pick 0, 1, 2, 3, or 4.

How does it work? Very simple! It hashes the filenames that nose is running through, does a modulo division by N, then sees if this file is "its". Very simple, but it lets you run multiple of these nose-picker enabled runners in parallel, each running a separate subset of the unit tests!

Motivation

The nose multiprocess plugin takes over the test runner when it runs, and thus is not amenable to environments where you need a custom test runner. nose-picker lets you keep your test runner!

Installing

Through pip:

pip install --user nose-picker

Sample Multiprocess Script

Something like:

def main():
    num_processes = int(multiprocessing.cpu_count() * 2.5)
    tests = []
    for i in range(num_processes):
        test_command = TEST_CMD_TEMPLATE % (
            i,
            num_processes,
        )
        tests.append(TestWatcher(test_command))

    returncode = 0
    for test_watcher in tests:
        test_watcher.join()
        if test_watcher.returncode > 0:
            returncode += test_watcher.returncode
        for line in test_watcher.stderr.splitlines():
            if not (
                line.endswith(' ... ok') or
                '... SKIP' in line
            ):
                sys.stderr.write(line + '\n')

    return returncode


class TestWatcher(threading.Thread):
    def __init__(self, command):
        super(TestWatcher, self).__init__()
        self.command = command
        self.stdout = ''
        self.stderr = ''
        self.start()
        self.returncode = 0

    def run(self):
        p = subprocess.Popen(
            self.command,
            shell=True,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
        )
        self.stdout, self.stderr = p.communicate()
        self.returncode = p.returncode