...par Cédric Krier pour les Geeks Anonymes du 30/11/2018

1. Test your code
Cédric Krier
http://www.b2ck.com/

2. 2
Who am I ?
●
B2CK shareholder
●
Developers (since 2001)
●
Tryton developers (for 10 years)

3. 3
Tryton source code

4. 4
Why writing tests?
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Correctness of code… now
●
Correctness of code… tomorrow
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Prevent past bugs to haunt you again
●
Give you confidence when refactoring

5. 5
How to write tests?
➔
Unit
➔
Integration
➔
Functional
➔
Generated
➔
Performance

6. 6
Testing good practices
➔
Isolated
➔
Reproducible / Deterministic
➔
Fast (if possible)
➔
Simple
➔
Automated (with CI)

7. 7
Test should be isolated
●
No interference between each test
●
Can run only one at a time
●
Can be run in parallel

8. 8
Test should be
reproducible/deterministic
●
Avoid “It works on my computer”
●
Static input:
– No random
– Date/Time: FreezeGun
– PYTHONHASHSEED

9. 9
Test should be fast

10. 10
Test should be fast
●
Developers should not hesitate to run
them
●
Allow to run the subsets targeting the
changes
●
Avoid:
– heavy computation
– slow network connection

11. 11
Test should be simple
●
Test your code, not your dependencies
●
Simple… but not trivial
– Test the behavior not the implementation
●
Simple enough to allow to fix failure
without debugging
●
Easier to maintain

12. 12
Test should be automated
●
Continuous Integration (Buildbot,
Jenkins, Drone etc.)
– Run on each commit (or pull request)
– Test on multiple environments (tox, docker, …)
– Feedback to author about failure
(responsibility)

13. 13
Tools for testing in Python
●
Test Case:
– unittest, doctest, mock
●
Test runners:
– unittest, pytest, nose, tox
●
Behavior driven development ⚠
– behave, lettuce
●
Generated tests
– hypothesis

14. 14
How testing?
➔
Unit
➔
Integration
➔
Functional
➔
Generated
➔
Performance

15. 15
Unit test
●
Testing smallest unit of code → the
function
●
Check output from defined input
(like a black box)

16. 16
Unit test good practices
●
Triple-A
– Arrange
– Act
– Assert

17. 17
Unit test good practices

18. 18
Unit test good practices
●
Limit usage of Mock
●
Do not bloat API for dependency
injection

19. 19
Unit test good practices

20. 20
Unit test in Python
●
Use explicit docstring
●
Use:
– assertEqual instead of assert(a == b)
– assertRaises (context manager)
– assertWarns, assertLogs
– assertListEqual, assertDictEqual, etc.
– addCleanup (register tearDown in setUp)

21. 21
Integration tests
●
Test interactions between components
●
Instead of testing internal parts,
test public API

22. 22
Integration test good practices
●
Don’t forget to clean up
●
Check absence of error instead of the
result

23. 23
Integration test in Python
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Use “setUp” and “tearDown”

24. 24
Functional test
●
Check behaviors as an end user
●
Run complete workflow, ex:
sale → shipment → invoice → payment

25. 25
Functional test good practices
●
Run with the full stack
– Database
– Network
– Access rights
●
Simulate user behavior
– Selenium
– RPC call

26. 26
Functional test for Python
●
Use doctest

27. 27
Functional test for Python
●
Selenium with Python

28. 28
Generated test
●
Test properties of output with random
input (but limited)
●
Try to break with fuzzy input

29. 29
Generated test good practices
●
Not included in CI
●
But run from time to time

30. 30
Generated test in Python
●
Hypothesis

31. 31
Performance test
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Measure time to make an action
– Warm-up (setup, cache etc.)
– Compare mean
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Test load capacity
– Fire a lot of requests

32. 32
Performance test in Python
●
timeit

33. 33
Performance test in Python
●
Boom

34. 34
Conclusion
Write enough tests to be confident
Do not write too much that will block
you