Pytest plugin to randomly order tests and control
available for nose).
All of these features are on by default but can be disabled with flags.
- Randomly shuffles the order of test items. This is done first at the level of modules, then at the level of test classes (if you have them), then at the order of functions. This also works with things like doctests.
random.seed()at the start of every test case and test to a fixed number - this defaults to
time.time()from the start of your test run, but you can pass in
--randomly-seedto repeat a randomness-induced failure.
- If factory boy is installed, its random state is reset at the start of every test. This allows for repeatable use of its random 'fuzzy' features.
- If faker is installed, its random state is reset at the start of every test. This is also for repeatable fuzzy data in tests - factory boy uses faker for lots of data.
- If numpy is installed, its random state is reset at the start of every test.
Randomness in testing can be quite powerful to discover hidden flaws in the tests themselves, as well as giving a little more coverage to your system.
By randomly ordering the tests, the risk of surprising inter-test dependencies is reduced - a technique used in many places, for example Google's C++ test runner googletest.
By resetting the random seed to a repeatable number for each test, tests can create data based on random numbers and yet remain repeatable, for example factory boy's fuzzy values. This is good for ensuring that tests specify the data they need and that the tested system is not affected by any data that is filled in randomly due to not being specified.
This plugin is a Pytest port of my plugin for nose,
Install from pip with:
pip install pytest-randomly
Pytest will automatically find the plugin and use it when you run
The output will start with an extra line that tells you the random seed that is
$ pytest platform darwin -- Python 2.7.11, pytest-2.9.1, py-1.4.31, pluggy-0.3.1 Using --randomly-seed=1460130750 ...
If the tests fail due to ordering or randomly created data, you can restart them with that seed using the flag as suggested:
Since the ordering is by module, then by class, you can debug inter-test pollution failures by narrowing down which tests are being run to find the bad interaction by rerunning just the module/class:
pytest --randomly-seed=1234 tests/module_that_failed/
You can disable behaviours you don't like with the following flags:
--randomly-dont-reset-seed- turn off the reset of
random.seed()at the start of every test
--randomly-dont-reorganize- turn off the shuffling of the order of tests
The plugin appears to Pytest with the name 'randomly'. To disable it
altogether, you can use the
-p argument, for example:
pytest -p no:randomly