--listTests should always print to stdout

[aaronabramov]

if we run jest with --listTests --json arguments the output will be printed to stderr which is incorrect.
We need to change these lines to use console.log https://github.com/facebook/jest/blob/master/packages/jest-cli/src/run_jest.js#L117-L122

also this test needs to be fixed to use stdout
https://github.com/facebook/jest/blob/master/integration_tests/__tests__/list_tests.test.js#L40-L42

[jseminck]

I'd like to tackle this!

[jseminck]

@aaronabramov does the else statement also need to be changed to use console.log?

Because if we force both outputs to be printed to console.log, then the argv.useStderr flag would not be taken into account anymore? Is that what you want? (if I understand the code correctly):

const outputStream = argv.json || argv.useStderr ? process.stderr : process.stdout;

It also specifically has this comment:

  // If we output a JSON object, we can't write anything to stdout, since
  // it'll break the JSON structure and it won't be valid.

See: https://github.com/facebook/jest/blob/master/packages/jest-cli/src/cli/index.js#L59

[aaronabramov]

@jseminck yep! that's exactly what the bug is :)
when we use --useStderr we redirect all "non data" output to stderr so that the "data" output does not get polluted.
and by "data output" i mean one of:

• JSON output when using --json
• JSON output when using --json --listTests
• \n separated list when using --listTests

so yes. both if and else should output to console.log while outputStream is used for everything else

[jseminck]

Thanks for the explanation! PR is up. 😄 Do we also need an additional test then to make sure --listTests --useStdErr is still printed to stdout ?

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