#pattern #python #testing
You need to test those two pesky lines at the end of your app, if you want 100% code coverage. For dynamically typed languages it is the absolute necessity to have 100% code coverage. Runtime type-checking will push all typos in names of functions and variables into runtime. You really need testtime protection against typos.
If you think that two untested lines of code at the end of your application wouldn't hurt you, just think about those:
1if __name__ == ‘_main__': # single underscore 2 main()
1if __name__ == ‘__main__': 2 sys.exit(main()) # forgot to import sys
1if __name__ == ‘__main__': 2 sys.exit(main) # forgot to call main
All of them will cause errors only in a runtime and they silently pass normal module import. So you need to test them. You need to execute them at the test stage, at least once.
How? Here is a link to show you all opinions on this topic: Stackoverflow question.
I used idea from one of answer to that question to create a comprehensive test for
Application code (module.py inside
Application code (
1import sys 2 3def main(): 4 print("Hello world!") 5 6def init(): 7 if __name__ == "__main__": 8 sys.exit(main()) 9 10init()
1import mock 2import pytest 3 4def test_init(): 5 from myapp import module 6 with mock.patch.object(module, "main", return_value=42): 7 with mock.patch.object(module, "__name__", "__main__"): 8 with mock.patch.object(module.sys,'exit') as mock_exit: 9 module.init() 10 assert mock_exit.call_args == 42
This rather bulky test assures that our init function does everything it should:
- Really calls main if we have
- Returns it return value as exit code
- Does not call main() otherwise.
The final line of the code, the
init() call will run at the module import time and, therefore, is run at testtime.
This gives us 100% code coverage provided we have tested
main() and the rest of the module code.
Credits to George Shuklin for the original article.
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