python config_error ai_generated true

test_output (tests.test_cli.TestCli) ... ok (no captured stdout shown despite print() in the test)

ID: python/unittest-buffer-stdout-lost

Also available as: JSON · Markdown · 中文
80%Fix Rate
83%Confidence
0Evidence
2024-06-30First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.10 active — — —
3.12 active — — —

Root Cause

unittest's buffer mode (`python -m unittest -b`) captures stdout/stderr and only prints it on failure; passing tests show nothing, so debugging prints are invisible.

generic

中文

unittest 的缓冲模式（`python -m unittest -b`）捕获 stdout/stderr 且仅在失败时打印；通过的测试不显示任何内容，调试打印不可见。

Workarounds

  1. 92% success 
    Disable buffering for the run:
python -m unittest -v tests.test_cli.TestCli
# or remove -b from the command / CI config
  2. 88% success 
    Or capture stdout explicitly with contextlib.redirect_stdout:
import io, contextlib
buf = io.StringIO()
with contextlib.redirect_stdout(buf):
    run_cli(['--help'])
self.assertIn('usage', buf.getvalue())

Dead Ends

Common approaches that don't work:

  1. 85% fail

    stderr is also captured by buffer mode; still hidden on pass.

  2. 90% fail

    Turns the test red; not usable for debugging passing tests.