HookHappens, the Python client

HookHappens ("Mock around & find out") stands in for the endpoints your system calls, or sits in front of the real ones. A test changes exactly the part of the answer it needs, and you see what your system did with it. The service lives at https://hookhappens.com; this package is the Python client and the pytest plugin for it.

pip install hookhappens

from hookhappens import HookHappens

with HookHappens("https://hookhappens.com", api_key="hh_…") as hh:
    with hh.new_namespace("snack-bar") as run:         # a throwaway address for this test run
        run.rule("order-snack", then=[{"status": 503}])  # the kitchen is on fire
        my_app.order("cookie", 3, kitchen=run.url)       # point your system at it
        call = run.wait_for("order-snack")               # the call your system made, with its answer
        assert call.status == 503

With pytest, the hh fixture does the same with no setup beyond two environment variables:

export HOOKHAPPENS_URL=https://hookhappens.com
export HOOKHAPPENS_API_KEY=hh_…
pytest

def test_the_kitchen_on_fire(hh):
    hh.scenario_on("kitchen-on-fire")
    my_app.order("cookie", 3, kitchen=hh.url)
    assert hh.wait_for(endpoint="order-snack").status == 503

The whole story, with a runnable example app and its test suite, is the Testing your system guide: https://hookhappens.com/#/how-to/testing. The service is hosted only; nothing to install but this client. © 2026 Carolina Shulman Grigoriev. All rights reserved.