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doc: add guidance on console output in tests

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PR-URL: https://github.com/nodejs/node/pull/26456
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Bryan English <bryan@bryanenglish.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
This commit is contained in:
Sam Roberts 2019-03-05 10:55:37 -08:00
parent 15e741a132
commit 4d89fcc6d6
1 changed files with 26 additions and 0 deletions
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doc/guides/writing-tests.md
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@ -281,6 +281,32 @@ assert.throws(
);
```
### Console output
Output written by tests to stdout or stderr, such as with `console.log()` or
`console.error()`, can be useful when writing tests, as well as for debugging
them during later maintenance. The output will be supressed by the test runner
(`./tools/test.py`) unless the test fails, but will always be displayed when
running tests directly with `node`. For failing tests, the test runner will
include the output along with the failed test assertion in the test report.
Some output can help debugging by giving context to test failures. For example,
when troubleshooting tests that timeout in CI. With no log statements, we have
no idea where the test got hung up. There have been cases where tests fail
without `console.log()`, and then pass when its added, so be cautious about its
use, particularly in tests of the I/O and streaming APIs.
Excessive use of console output is discouraged as it can overwhelm the display,
including the Jenkins console and test report displays. Be particularly
cautious of output in loops, or other contexts where output may be repeated many
times in the case of failure.
In some tests, it can be unclear whether a `console.log()` statement is required
as part of the test (message tests, tests that check output from child
processes, etc.), or is there as a debug aide. If there is any chance of
confusion, use comments to make the purpose clear.
### ES.Next features
For performance considerations, we only use a selected subset of ES.Next