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https://github.com/sobolevn/heisenbug-2019
Examples for Heisenbug 2019
https://github.com/sobolevn/heisenbug-2019
code-quality conference mutation-testing mutmut python talk testing
Last synced: 21 days ago
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Examples for Heisenbug 2019
- Host: GitHub
- URL: https://github.com/sobolevn/heisenbug-2019
- Owner: sobolevn
- Created: 2019-02-27T16:24:03.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2019-04-18T10:41:51.000Z (over 5 years ago)
- Last Synced: 2024-10-08T15:46:15.972Z (about 1 month ago)
- Topics: code-quality, conference, mutation-testing, mutmut, python, talk, testing
- Language: Jupyter Notebook
- Homepage:
- Size: 94.7 KB
- Stars: 12
- Watchers: 5
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Heisenbug 2019
[](https://wemake.services)
[](https://travis-ci.org/sobolevn/heisenbug-2019)
[](https://coveralls.io/github/sobolevn/heisenbug-2019?branch=master)
[](https://github.com/sobolevn/heisenbug-2019)
Demo app that shows how can we effectively use mutation testing.
## Contents
### missing_assert.py
This is a very basic example of test that does not do anything.
Because we have missed that our `assert` is commented out by accident!
```
⠙ 2/2 🎉 0 ⏰ 0 🤔 0 🙁 2
```
To solve this, just uncomment the `assert` in [test_missing_assert.py](https://github.com/sobolevn/heisenbug-2019/blob/master/tests/test_missing_assert.py)
### simple.py
This example is used to illustrate the simplest use-case possible.
We only have one function with a single statement.
This statement will be mutated, our mutation test will catch that.
```
⠼ 1/1 🎉 0 ⏰ 0 🤔 0 🙁 1
```
The solution to this case is available here: [test_simple.py](https://github.com/sobolevn/heisenbug-2019/blob/master/tests/test_simple.py)
### constants.py
Using the same constants for testing and production
does not actually test anything.
```
⠇ 6/6 🎉 2 ⏰ 0 🤔 1 🙁 3
```
Since we will miss cases like this one:
```diff
--- heisenbug/constants.py
+++ heisenbug/constants.py
@@ -1,7 +1,7 @@
# -*- coding: utf-8 -*-
-BAD_FUNCTION_NAMES = ['dir', 'vars', 'locals', 'globals']
+BAD_FUNCTION_NAMES = ['dir', 'vars', 'locals', 'XXglobalsXX']
```
The tests will move in sync with the production code, following the bugs introduced there!
Solution: duplicate your constants in tests, see [test_constants.py](https://github.com/sobolevn/heisenbug-2019/blob/master/tests/test_constants.py)
### flask_app.py
This example represents a regular `flask` application.
It is configured to swallow exceptions and log them somewhere.
It seems to be fully tested, but has one big mistake inside.
```
⠋ 10/10 🎉 2 ⏰ 0 🤔 0 🙁 8
```
This is the case we are looking for:
```diff
--- heisenbug/flask_app.py
+++ heisenbug/flask_app.py
@@ -18,7 +18,7 @@
@app.route('/{int:index}')
def hello(index):
"""View that will fail in production."""
- return 'Hello, world! {0} faith in you.'.format(1 * index)
+ return 'Hello, world! {0} faith in you.'.format(1 / index)
```
Since we swallow exceptions and test only partial of our output,
we will never be able to find the problem of when input is zero and causes a divide by zero.
Main take-away: high-level integrations tests are not good enough on their own.
Solution: do not use `200` code where something goes wrong,
make sure that you write enough unit-tests for your view logic.
### algorithm.py
This is a simple `bubble_sort` algorithm.
I have taken an example algorithm as is from [`TheAlgorithms/Python`](https://github.com/TheAlgorithms/Python/blob/master/sorts/bubble_sort.py),
which is a very popular `python` library.
This is the result (please, take a not that it has several false positives):
```
⠼ 20/20 🎉 15 ⏰ 0 🤔 0 🙁 5
```
You can see that we even use property-based tests [here](https://github.com/sobolevn/heisenbug-2019/blob/master/tests/test_algorithm.py).
But it still does not save us from the false-positives of mutation testing.
Main take-away: it is really hard to use mutation testing
to test algorithms built with performance and optimisations in mind.
### opensource_disl_case.ipynb
This is a real-world example about
my open-source project called [`docker-image-size-limit`](https://github.com/wemake-services/docker-image-size-limit).
It is a perfectly working app with just 70 lines for simple `python` code.
Fully tested with E2E and unit tests, typed, 100% covered.
And it has [~10 surviving mutants](https://github.com/sobolevn/heisenbug-2019/blob/master/heisenbug/opensource_disl_case.ipynb).
```
⠇ 29/29 🎉 19 ⏰ 0 🤔 2 🙁 8
```
This article shows you exactly what happened and how to solve this case.
## Resources
Here I have collected different resource that you might also be interested in.
### Articles
- https://hackernoon.com/mutmut-a-python-mutation-testing-system-9b9639356c78
- https://nedbatchelder.com/blog/201903/mutmut.html
### Talks
- https://vimeo.com/191364978
- https://vimeo.com/171319754
## License
Content is licensed under [CC BY-NC](https://creativecommons.org/licenses/by-nc/4.0/)