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Plugin for nose or pytest that automatically reruns flaky tests.

Project description

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About

Flaky is a plugin for nose or pytest that automatically reruns flaky tests.

Ideally, tests reliably pass or fail, but sometimes test fixtures must rely on components that aren’t 100% reliable. With flaky, instead of removing those tests or marking them to @skip, they can be automatically retried.

For more information about flaky, see this presentation.

Marking tests flaky

To mark a test as flaky, simply import flaky and decorate the test with @flaky:

from flaky import flaky
@flaky
def test_something_that_usually_passes(self):
    value_to_double = 21
    result = get_result_from_flaky_doubler(value_to_double)
    self.assertEqual(result, value_to_double * 2, 'Result doubled incorrectly.')

By default, flaky will retry a failing test once, but that behavior can be overridden by passing values to the flaky decorator. It accepts two parameters: max_runs, and min_passes; flaky will run tests up to max_runs times, until it has succeeded min_passes times. Once a test passes min_passes times, it’s considered a success; once it has been run max_runs times without passing min_passes times, it’s considered a failure.

@flaky(max_runs=3, min_passes=2)
def test_something_that_usually_passes(self):
    """This test must pass twice, and it can be run up to three times."""
    value_to_double = 21
    result = get_result_from_flaky_doubler(value_to_double)
    self.assertEqual(result, value_to_double * 2, 'Result doubled incorrectly.')

Marking a class flaky

In addition to marking a single test flaky, entire test cases can be marked flaky:

@flaky
class TestMultipliers(TestCase):
    def test_flaky_doubler(self):
        value_to_double = 21
        result = get_result_from_flaky_doubler(value_to_double)
        self.assertEqual(result, value_to_double * 2, 'Result doubled incorrectly.')

    @flaky(max_runs=3)
    def test_flaky_tripler(self):
        value_to_triple = 14
        result = get_result_from_flaky_tripler(value_to_triple)
        self.assertEqual(result, value_to_triple * 3, 'Result tripled incorrectly.')

The @flaky class decorator will mark test_flaky_doubler as flaky, but it won’t override the 3 max_runs for test_flaky_tripler (from the decorator on that test method).

Pytest marker

When using pytest, @pytest.mark.flaky can be used in place of @flaky.

Don’t rerun certain types of failures

Depending on your tests, some failures are obviously not due to flakiness. Instead of rerunning after those failures, you can specify a filter function that can tell flaky to fail the test right away.

def is_not_crash(err, *args):
    return not issubclass(err[0], ProductCrashedError)

@flaky
def test_something():
    raise ProductCrashedError

@flaky(rerun_filter=is_not_crash)
def test_something_else():
    raise ProductCrashedError

Flaky will run test_something twice, but will only run test_something_else once.

It can also be used to incur a delay between test retries:

import time

def delay_rerun(*args):
    time.sleep(1)
    return True

@flaky(rerun_filter=delay_rerun)
def test_something_else():
    ...

Activating the plugin

Like any nose plugin, flaky can be activated via the command line:

nosetests --with-flaky

With pytest, flaky will automatically run. It can, however be disabled via the command line:

pytest -p no:flaky

Command line arguments

No Flaky Report

Pass --no-flaky-report to suppress the report at the end of the run detailing flaky test results.

Shorter Flaky Report

Pass --no-success-flaky-report to suppress information about successful flaky tests.

Force Flaky

Pass --force-flaky to treat all tests as flaky.

Pass --max-runs=MAX_RUNS and/or --min-passes=MIN_PASSES to control the behavior of flaky if --force-flaky is specified. Flaky decorators on individual tests will override these defaults.

Additional usage examples are in the code - see test/test_nose/test_nose_example.py and test/test_pytest/test_pytest_example.py

Installation

To install, simply:

pip install flaky

Compatibility

Flaky is tested with the following test runners and options:

  • Nosetests. Doctests cannot be marked flaky.

  • Py.test. Works with pytest-xdist but not with the –boxed option. Doctests cannot be marked flaky.

Contributing

See CONTRIBUTING.rst.

Setup

Create a virtual environment and install packages -

mkvirtualenv flaky
pip install -r requirements-dev.txt

Testing

Run all tests using -

tox

The tox tests include code style checks via pycodestyle and pylint.

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