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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Prevent prefix \"called_\" for methods on mock objects in safe mode","articleBody":"# Prevent prefix \"called_\" for methods on mock objects in safe mode\r\n\r\n# Pitch\r\n\r\nIn safe mode, there's already support for catching typos for accessing the assertion methods:\r\n\r\n\u003e By default, accessing any attribute whose name starts with assert, assret, asert, aseert or assrt will raise an AttributeError.\r\n\r\nGiven you have a valid assertion to check whether a mocked function has been called:\r\n```\r\nassert mock_foo.called\r\n```\r\n\r\nIf you now want to check the arguments, and do not pay full attention, you can end up with a tautology like\r\n\r\n```\r\nassert mock_foo.called_once_with(param=\"test\")\r\n```\r\n\r\nThe issue: `mock_foo.called_once_with` is not a valid (assertion) method and therefore an instance of mock.Mock is returned. Because instances of mock.Mock evaluate to true, the assertion is equivalent to `assert True`.\r\nLike with the preventing the call of methods that start with `assert` and `assret` ([issue 21238](https://bugs.python.org/issue21238)) and also disallowing the typos `asert`, `aseert`, and  `assrt` (https://github.com/python/cpython/pull/23165), this error will not cause a test failure.\r\n\r\nAnalyzing public repositories on github.com, the Python standard library (thanks @terryjreedy for fixing it in https://github.com/python/cpython/pull/100647), and our internal code base revealed what seems to be a common source of errors. In our own code base, we have had more than 500 of these issues. More than 50% of those failed after fixing the assertion call, which could potentially have covered existing bugs by relying on bad tests.\r\n\r\n# Previous discussion\r\n\r\nhttps://discuss.python.org/t/include-prefix-called-in-list-of-forbidden-method-prefixes-for-mock-objects-in-unsafe-mode/22249/4\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-100691\n* gh-100819\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/cklein","@type":"Person","name":"cklein"},"datePublished":"2023-01-02T15:51:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/100690/cpython/issues/100690"}