Provide a way to stop locust test when there are problems during on_test_start() event

[sfc-gh-tlasica]

Context:
Before starting benchmark I would like to prepare some data e.g. setup in the database some unique table with data
If this setup fails (for any reason) I do not want to continue, I do not even want to start users
I have used event on_test_start() for this setup (maybe incorrectly?)

Problem:
I do not see how to achieve that.
Raising LocustError() from on_test_start() does not help - seems the exception is swallowed.

Idea
Maybe this event should be able to return boolean to denote if the test should continue?

[cyberw]

You should be able to call self.environment.runner.quit() - try it out!

[sfc-gh-tlasica]

hmmm, but the on_test_start() functions are not in the user context, correct?
they are declared on the module (file) level?
sorry if I am not understanding something here or doing something non-idiomatic.

[cyberw]

Ah, I was thinking of User.on_start. Are you talking about the test_start event? Try something like this:

@events.test_start.add_listener
def on_test_start(environment, **_kwargs):
    # do stuff
    if something_went_wrong:
         environment.runner.quit()

[sfc-gh-tlasica]

This works to some extent:

import os

from locust import events, task, between
from locust.user import HttpUser


@events.test_start.add_listener
def on_test_start(environment, **kwargs):
    if os.environ.get("FAIL", "0") == "1":
        logging.error("Benchmark preparation FAILED:")
        environment.runner.quit()


class DummyUser(HttpUser):
    wait_time = between(1, 3)

    @task
    def get_ip_jsontest_com(self):
        self.client.get("http://ip.jsontest.com/")

Kind of works: indeed users are not started, but process does not end.

My goal is to fail benchmark early if preparation step failed.

python -m locust --host null -f fail-on-task-start.py --autostart --headless

[cyberw]

that should definitely end the process, is there an error message?

if it doesnt work, you can always just kill the process:

os._exit(1)