Items tagged python, testing in 2024
Filters: Year: 2024 × python × testing × Sorted by date
inline-snapshot. I'm a big fan of snapshot testing, where expected values are captured the first time a test suite runs and then asserted against in future runs. It's a very productive way to build a robust test suite.
inline-snapshot by Frank Hoffmann is a particularly neat implementation of the pattern. It defines a snapshot() function which you can use in your tests:
assert 1548 * 18489 == snapshot()
When you run that test using pytest --inline-snapshot=create the snapshot() function will be replaced in your code (using AST manipulation) with itself wrapping the repr() of the expected result:
assert 1548 * 18489 == snapshot(28620972)
If you modify the code and need to update the tests you can run pytest --inline-snapshot=fix to regenerate the recorded snapshot values. # 16th April 2024, 4:04 pm
time-machine example test for a segfault in Python (via) Here’s a really neat testing trick by Adam Johnson. Someone reported a segfault bug in his time-machine library. How you you write a unit test that exercises a segfault without crashing the entire test suite?
Adam’s solution is a test that does this:
subprocess.run([sys.executable, “-c”, code_that_crashes_python], check=True)
sys.executable is the path to the current Python executable—ensuring the code will run in the same virtual environment as the test suite itself. The -c option can be used to have it run a (multi-line) string of Python code, and check=True causes the subprocess.run() function to raise an error if the subprocess fails to execute cleanly and returns an error code.
I’m absolutely going to be borrowing this pattern next time I need to add tests to cover a crashing bug in one of my projects. # 23rd March 2024, 7:44 pm