python runtime_error ai_generated true

AssertionError: 3 != 5 : expected 5 but got 3

ID: python/unittest-assert-equal-order

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-01-22First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.10 active — — —
3.12 active — — —

Root Cause

In unittest, `assertEqual(first, second)` reports the message as `first != second`. Developers often read the message right-to-left and fix the wrong side of the assertion, or assume the function under test is broken when the arguments were swapped.

generic

中文

在 unittest 中，`assertEqual(first, second)` 报告的消息格式是 `first != second`。开发者常把消息从右往左读，从而修改了断言错误的一侧，或误以为被测函数有问题，而实际是参数顺序写反了。

Workarounds

  1. 95% success 
    Always put the actual value first and add a msg for clarity:

self.assertEqual(result, 5, f'unexpected result: {result!r}')
  2. 98% success 
    Use pytest's rich assertion rewriting instead, which prints both operands clearly:

assert result == 5

Dead Ends

Common approaches that don't work:

  1. 60% fail

    The test expectation was reversed; changing production code introduces a bug to satisfy a wrong assertion.

  2. 90% fail

    Silences the test and hides real regressions; the CI still reports green while behavior is wrong.