v8/test/message/README.md

# JavaScript tests with expected output

Tests in `test/message` pass if the output matches the expected output.
Message tests are particularly useful when checking for exact error messages.

Tests and their expected output must have the same filename, with the `.js` and
`.out` extension.

```
foo.js
foo.out
```

You can use a regex in the expected output instead of the exact
path:

```
*%(basename)s:7: SyntaxError: Detected cycle while resolving name 'a'
```

Empty lines are ignored in the comparison, but whitespaces are not.

Exact details of the test runner are in [testcfg.py](testcfg.py).