Automated, comprehensive and well-organised pytest test cases.
Automated, comprehensive and well-organised pytest test cases.
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pip install pytest_cleanup
If we like to format our code with tools like Black, then why don't we do the same with our tests?
pytest_cleanup runs your Python code and generates pytest tests out of it.
This will help you reach broad test coverage with real-world test cases. Tests that are generated "just work", i.e they are clean, unaware of implementation details, and don't require active maintenance.
It even generates the (minimal) code that it requires to work; just 2 test functions (one for async and another for normal functions). These 2 are then parameterised with the parametrize feature via
The data files are written with
jsonpickle and look like this:
It's also possible to run it against an existing pytest test suite (see below).
In other words, it lets you do DDT for pytest (data-driven tests, development-driven testing, or both :nerd_face:)
Why would you bother?
- save time by having tests generated for you :tada:
- dramatically increase test code coverage with little effort
- write more maintainable tests by separating code and data
- Too tedious/hard to generate custom data for your application? Run your code like you would in production and data files will be generated.
- helps you organise your test code consistently in new projects, or:
- replace your existing disorganised test code :+1:
- reduces handwritten setup code
- accelerate your migration to pytest; Since pytest supports existing nose and unittest, enable the recorder, run pytest and
pytest_cleanupwill generate clean tests for you.
Note that tests that you write manually can still be kept or made to follow the same conventions as pytest_cleanup for consistency
How it works
pytest_cleanup generates 3 files. These contain the minimal boilerplate required in your test (or current) directory:
2020-01-25 15:36:34.614 | DEBUG | pytest_cleanup.constants:get_test_dir:18 - Will place test_pytestcleanup_cases.py under /app/test 2020-01-25 15:36:34.614 | INFO | pytest_cleanup.recorder:__init__:252 - creating instance of recorder 2020-01-25 15:36:34.692 | DEBUG | pytest_cleanup.recorder:save_example_scripts:159 - Saving example scripts (test_pytestcleanup_cases.py, conftest-pytest-cleanup-runtime.py, conftest-pytest-cleanup-record.py) under test
This will have the following 2 tests:
import pytest from pytest_cleanup.common import assert_return_values def test_pytest_cleanup_sync_test_cases(fn, args, kwargs, expected): """See test/test-data directory for test cases""" actual = fn(*args, **kwargs) assert_return_values(actual, expected) @pytest.mark.asyncio async def test_pytest_cleanup_async_test_cases(fn, args, kwargs, expected): """See test/test-data directory for test cases. support for asyncio in pytest may be enabled by installing pytest-asyncio """ actual = await fn(*args, **kwargs) assert_return_values(actual, expected)
The latter will be parametrized with the data files that will be generated later under
$your_test_directory/test-data. This is achieved with snippet found with the also generated:
conftest-pytest-cleanup-runtime.py (rename it to conftest.py or merge it with your existing conftest.py so that pytest can load it):
def pytest_generate_tests(metafunc): from pytest_cleanup import parametrize_stg_tests parametrize_stg_tests(metafunc)
The third file that is generated is
conftest-pytest-cleanup-record.py. You can use this one in case you want to use
pytest_cleanup against an existing pytest test suite (see previous section on why you might want that):
Again, rename it to conftest.py or merge it with your existing conftest.py so that pytest can load it
from pytest_cleanup import Recorder def pytest_runtestloop(session): Recorder().enter() def pytest_sessionfinish(session, exitstatus): Recorder().exit()
There are 3 ways to use
- Record your tests
python -m pytest_cleanup your.module.path(an importable module path, not file path!). This will attempt to call a no-arg function named
mainin the module specified. (Function name configurable; see configuration section).
pytest_cleanupwill record function invocations and save them
- Put generated
conftest-pytest-cleanup-runtime.pyinto your conftest.py
- Run pytest as you normally would. It will load generated data by step 1 under
$test_directory/test-dataand dynamically generate test cases from it.
- Confirm your test run passes.
Use as a library
pytest_cleanup can also be used as a library for more flexibility. Otherwise, it's only needed as a test dependency.
from pytest_cleanup import Recorder with Recorder(): your_custom_code_here()
Run pytest as explained in previous subsection.
Note that the
Recorderobject is a singleton and invoking
Recorder()multiple times has no effect.
Using while running pytest
You can also run
pytest_cleanup against an existing test suite:
python -m pytest_cleanup
- Put generated
conftest-pytest-cleanup-record.pyinto your conftest.py. (it has the functions
pytest_sessionfinishto be able to record in pytest sessions)
- Run pytest as you normally would
- In conftest.py, replace
pytest_sessionfinishfunctions by the contents of
conftest-pytest-cleanup-runtime.py(which has the
- Handles functions that return generators by automatically extending these into Python lists so that they can be asserted.
- Support for asyncio coroutines
- Supports nested (local) functions with
dilllibrary (appears as base64-encoded in the json files)
- Removes duplicate test cases (i.e identical arguments that return identical return values)
The botostubs (by yours truly) went from 0 to 71% adopting pytest_cleanup:
-- Docs: https://docs.pytest.org/en/latest/warnings.html ---------- coverage: platform linux, python 3.6.10-final-0 ----------- Name Stmts Miss Cover Missing --------------------------------------- main.py 208 60 71% 93, 133, 161, 179-184, 191, 199-210, 214-248, 296-297, 305-310, 314-316, 320-322, 326
- Running over and over write test cases in new files to avoid overwriting your previous test cases. The filenames are appended with -00, -01, ... for up to 10 files.
- It works well if your functions are deterministic (e.g pure).
If not, then you should probably make them so!
- If your function arguments are not serialisable, then test cases won't be generated. You will see an error in the logs for that function.
- This project uses pickling (with jsonpickle or dill) to load the test data. If you're the one generated test data, then it should be fine loading it during tests. Otherwise, don't load untrusted test data.
pytest_cleanup is configurable exclusively via environment variables:
PYTESTCLEANUP_LOG_LEVEL: Set to DEBUG to investigate/report issues.
PYTESTCLEANUP_TEST_DATA_DIRECTORY: Change it the default (
test-data) is inconvenient.
PYTESTCLEANUP_TEST_DIRECTORY: Specify your test directory explicitly. By default, will check in order:
testing, or otherwise assumes the current directory.
PYTESTCLEANUP_FUNCTION: If you invoke
python -m pytest_cleanup your.module, it will invoke its no-arg
mainby default. Set this env var to change it.
PYTESTCLEANUP_TEST_CASE_COUNT_PER_FUNCTION: By default, will record 5 test cases per function.
PYTESTCLEANUP_SERIALISATION_DEPTH: Decrease it in case you get a maximum recursion depth exception while deserialising. Default 500.
PYTESTCLEANUP_FILESIZE_LIMIT_MB: Limit the json content size. Useful if you don't want to get big test data files. Default: 5 MB.
PYTESTCLEANUP_INCLUDE_MODULES: Force include certain modules from consideration. Some modules are excluded by default (those installed in the virtualenv, built-in functions and other system packages). Accepts wildcard patterns via fnmatch Takes precedence over
PYTESTCLEANUP_EXCLUDE_MODULES: Force exclude certain modules from consideration.
PYTESTCLEANUP_ALLOW_ALL_MODULES: Force considers all modules. Warning: slow!
- Minor issue: functions in your main module may be loaded twice, creating identical test cases twice for that function. (maybe happening only in this project)
- Handle test suites that are run in
tox. The test files generated are in tox's virtualenv temp directory and we need a way to get them out of it so that tox can use them in subsequent runs.
- Since we now have example test cases, we could increase their value by generating property-based tests out of them with Hypothesis. If anybody is interested in picking this up, let me know.
What if you have test failures?
It may be due to a bug in pytest_cleanup but it's probably because it's difficult to serialise all data types, e.g file descriptors.
Cases that you should handle on your own
- Problem: Assertion does not work properly on your objects
Solution: You should define an
__eq__function in your class. This will ensure that pytest asserts the return values properly.
How to report in issue
- Raise an issue here about the test failure (or upvote an existing one)
- Paste your function code (or its signature)
- Paste the json file that
- State what you were expecting
- State what happened instead
Thanks to the following projects for making this possible:
But also huge thanks to the pytest team for making the most exciting test framework that I've ever seen. Other libraries used:
- flit (packaging and deployment to PyPI)
- loguru (logging)
- pytest plugins like pytest-progress, pytest-asyncio, pytest-randomly, pytest-cov
- sceptre (for deploying to aws)
These projects resemble this one but mine requires much less effort on your part and generates even less boilerplate :+1:
Copyright 2020. Jeshan G. BABOOA Released under the MIT licence. See file named LICENCE for details.
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