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.