Package: pytest-mock-generator
pytest-mock-generatorA pytest fixture wrapper forhttps://pypi.org/project/mock-generatorInstallationpipinstallpytest-mock-generatoror install withpoetry:poetryaddpytest-mock-generatorUsageThispytest pluginadds themgfixturewhich helps when writing tests that usepython mocks.Let's start with an easy example. Assume you have a module namedtested_module.pywhich holds a function
to process a string sent to it and then add it to a zip file:importzipfiledefprocess_and_zip(zip_path,file_name,contents):processed_contents="processed "+contents# some complex logicwithzipfile.ZipFile(zip_path,'w')aszip_container:zip_container.writestr(file_name,processed_contents)This is the function that you want to test (aka Unit Under Test or UUT).
You don't want to create a file on the hard drive and wish to mock it instead.Although this is a very short function,
writing the test code takes a lot of time. It's the fact that the function uses
a context manager makes the testing more complex than it should be.If you don't believe me, try to manually write mocks and asserts which verify
thatzip_container.writestrwas called with the right parameters.Generating the 'Arrange' and 'Assert' sections using Mock GeneratorTo generate the 'Arrange' and 'Assert' sections, simply put this code at the beginning of
your test function skeleton and run it (make sure to add themgfixture):fromtests.sample.code.tested_moduleimportprocess_and_zipdeftest_process_and_zip(mocker,mg):# arrange: todomg.generate_uut_mocks_with_asserts(process_and_zip)# act: invoking the tested codeprocess_and_zip('/path/to.zip','in_zip.txt','foo bar')# assert: todoThis will generate the sections for you:# mocked dependenciesmock_ZipFile=mocker.MagicMock(name='ZipFile')mocker.patch('tests.sample.code.tested_module.zipfile.ZipFile',new=mock_ZipFile)# calls to generate_asserts, put this after the 'act'mg.generate_asserts(mock_ZipFile,name='mock_ZipFile')The generated code is returned, printed to the console and also copied to the
clipboard for your convenience.
Just paste it (as simple as ctrl+V) to your test function:fromtests.sample.code.tested_moduleimportprocess_and_zipdeftest_process_and_zip(mocker,mg):# arrange:# mocked dependenciesmock_ZipFile=mocker.MagicMock(name='ZipFile')mocker.patch('tests.sample.code.tested_module.zipfile.ZipFile',new=mock_ZipFile)# act: invoking the tested codeprocess_and_zip('/path/to.zip','in_zip.txt','foo bar')# assert: todo# calls to generate_asserts, put this after the 'act'mg.generate_asserts(mock_ZipFile,name='mock_ZipFile')Excellent! Arrange section is ready. Run the test function once more to get the asserts:assert1==mock_ZipFile.call_countmock_ZipFile.assert_called_once_with('/path/to.zip','w')mock_ZipFile.return_value.__enter__.assert_called_once_with()mock_ZipFile.return_value.__enter__.return_value.writestr.assert_called_once_with('in_zip.txt','processed foo bar')mock_ZipFile.return_value.__exit__.assert_called_once_with(None,None,None)Wow, that's a handful of asserts! Some are very useful:Checking that we opened the zip file with the right parameters.Checking that we wrote the correct data to the proper file.Finally, ensuring that__enter__and__exit__are called, so there
are no open file handles which could cause problems.You can remove any generated lines which you find unnecessary.Paste that code right after the act phase, and you're done!The complete test function:fromtests.sample.code.tested_moduleimportprocess_and_zipdeftest_process_and_zip(mocker):# arrange:# mocked dependenciesmock_ZipFile=mocker.MagicMock(name='ZipFile')mocker.patch('tests.sample.code.tested_module.zipfile.ZipFile',new=mock_ZipFile)# act: invoking the tested codeprocess_and_zip('/path/to.zip','in_zip.txt','foo bar')# assert:assert1==mock_ZipFile.call_countmock_ZipFile.assert_called_once_with('/path/to.zip','w')mock_ZipFile.return_value.__enter__.assert_called_once_with()mock_ZipFile.return_value.__enter__.return_value.writestr.assert_called_once_with('in_zip.txt','processed foo bar')mock_ZipFile.return_value.__exit__.assert_called_once_with(None,None,None)Can you imagine the time it would have taken you to code this on your own?What's NextAsserting Existing MocksAt times, you may be editing a test function already containing mocks, or
you choose to write the mocks yourself, to gain some extra control.Mock Generator can generate the assert section for standard
Python mocks, even if they were not created using the Mock Generator.Put this after the 'Act' (replacemock_objwith your mock object name):mg.generate_asserts(mock_obj)Take the generated code and paste it at the 'Assert' section.TroubleshootingNo output is printed to the console when running PytestBe sure to run Pytest with appropriate flags to print the output:pytest -rA.No output is copied to the clipboardMock Generator usespyperclipfor clipboard
manipulations, look for errors / warnings printed to the console, similar to this one:WARNING mock_autogen.utils:utils.py:28 
Could not copy func results to clipboard Traceback (most recent call last): 
    File "/home/username/Documents/code/test_mock_gen/.envtest/lib/python3.6/site-packages/mock_autogen/utils.py", line 25, in to_clipboard 
        pyperclip.copy(result) 
    File "/home/username/Documents/code/test_mock_gen/.envtest/lib/python3.6/site-packages/pyperclip/__init__.py", line 659, in lazy_load_stub_copy 
        return copy(text) 
    File "/home/username/Documents/code/test_mock_gen/.envtest/lib/python3.6/site-packages/pyperclip/__init__.py", line 336, in __call__
        raise PyperclipException(EXCEPT_MSG) pyperclip.PyperclipException: 
        
    Pyperclip could not find a copy/paste mechanism for your system. 
    For more information, please visit https://pyperclip.readthedocs.io/en/latest/index.html#not-implemented-errorIt's possible that your system lacks some dependency, visithttps://pyperclip.readthedocs.io/en/latest/index.html#not-implemented-errorfor
additional troubleshooting steps.More informationAdditional documentation can be found in themock-generator pypi.📈 ReleasesYou can see the list of available releases on theGitHub Releasespage.We followSemantic Versionsspecification.🛡 LicenseThis project is licensed under the terms of theMITlicense. SeeLICENSEfor more details.📃 Citation@misc{pytest-mock-generator,author={Peter Kogan},title={A pytest fixture wrapper for https://pypi.org/project/mock-generator},year={2021},publisher={GitHub},journal={GitHub repository},howpublished={\url{https://github.com/pksol/pytest-mock-generator}}}CreditsThis project was generated withpython-package-template