https://github.com/wimglenn/copyingmock

A subclass of MagicMock that copies the arguments
https://github.com/wimglenn/copyingmock

Last synced: 3 months ago
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A subclass of MagicMock that copies the arguments

• Host: GitHub
• URL: https://github.com/wimglenn/copyingmock
• Owner: wimglenn
• License: mit
• Created: 2016-12-06T04:10:06.000Z (over 8 years ago)
• Default Branch: main
• Last Pushed: 2024-11-05T03:00:10.000Z (8 months ago)
• Last Synced: 2025-03-23T19:22:22.834Z (3 months ago)
• Language: Python
• Size: 11.7 KB
• Stars: 6
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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# Copying Mock

`MagicMock` has problems when used on a function with mutable arguments.

This is called out in the [documentation](https://docs.python.org/3/library/unittest.mock-examples.html#coping-with-mutable-arguments):

> Another situation is rare, but can bite you, is when your mock is

> called with mutable arguments. `call_args` and `call_args_list` store

> references to the arguments. If the arguments are mutated by the code

> under test then you can no longer make assertions about what the

> values were when the mock was called.

They then go on to propose a workaround, using `side_effect`, but it's

not very likable. There is also an elegant recipe offered which copies

arguments at call-time. It's simply a subclass of `MagicMock` which

copies the arguments, instead of storing references. I'm not sure why

the recipe wasn't included directly in `mock`, so here it is as a

third-party package.