Build Tooling: Collapse or omit successful test results from Travis build

[aduth]

In order to reduce contributor friction resulting from a failing build, we should seek to keep build results as actionable as possible. A failing Jest build is difficult to decipher because it includes potentially thousands of passing test cases. In these situations, usually only the failed test is relevant for the contributor.

Example: https://travis-ci.com/WordPress/gutenberg/jobs/211276270

Task: Logging for successful tests should be silenced or collapsed.

Relevant Details:

• Travis internally uses special prefixes for its own logging collapsing, travis_fold:start:FOO and travis_fold:end:FOO (example). These could be used for collapsing log output of the successful test cases.
• PHPUnit tests "show" all tests run, but simply display a "." dot character for the successful tests (example)
• At a glance, Jest CLI options don't appear to support this use-case, but we could use a custom reporter to customize the output (e.g. jest-silent-reporter, jest-simple-dot-reporter)

[epiqueras]

https://github.com/rickhanlonii/jest-silent-reporter works well. Should we just add that?

[aduth]

https://github.com/rickhanlonii/jest-silent-reporter works well. Should we just add that?

It seems like a good option.

[epiqueras]

A folding one would be better, but I can't find one.

[aduth]

A folding one would be better, but I can't find one.

It's maybe needlessly complex, but there might be something with:

1. Use jest-standard-reporter to partition logging between stdout and stderr
2. Redirect outputs to two files for stdout and stderr
3. Echo the contents of stdout file between the Travis start and end tags for folding
4. Echo the contents of stderr file outside/after the folded success output
5. Delete the files

[epiqueras]

I'd rather build a reporter that does that instead of hacking it in a script that creates files.