Testing javascript with Mocha - how can I use console.log to debug a test?

Question

I am using the javascript test-runner \"Mocha\".

I have a test that is failing, so I would to debug it using console.log.

But when the tests are

Answer 1

I had an issue with node.exe programs like test output with mocha.

In my case, I solved it by removing some default "node.exe" alias.

I'm using Git Bash for Windows(2.29.2) and some default aliases are set from /etc/profile.d/aliases.sh,

  # show me alias related to 'node'
  $ alias|grep node
  alias node='winpty node.exe'`

To remove the alias, update aliases.sh or simply do

unalias node

I don't know why winpty has this side effect on console.info buffered output but with a direct node.exe use, I've no more stdout issue.

Answer 2

Use the debug lib.

import debug from 'debug'
const log = debug('server');

Use it:

log('holi')

then run:

DEBUG=server npm test

And that's it!

Answer 3

If you are testing asynchronous code, you need to make sure to place done() in the callback of that asynchronous code. I had that issue when testing http requests to a REST API.

Answer 4

You may have also put your console.log after an expectation that fails and is uncaught, so your log line never gets executed.

Answer 5

What Mocha options are you using?

Maybe it is something to do with reporter (-R) or ui (-ui) being used?

console.log(msg);

works fine during my test runs, though sometimes mixed in a little goofy. Presumably due to the async nature of the test run.

Here are the options (mocha.opts) I'm using:

--require should
-R spec
--ui bdd

Hmm..just tested without any mocha.opts and console.log still works.