Logging only in `fit` mode

Do you want to request a feature or report a bug?

Feature

I often add debug logging in my programs, which I’d like to see in one specific case: fit() (focus-it) annotated tests, but I usually end up doing something like if (global.JEST_IS_FIT) console.log(x) in my source code, and global.JEST_IS_FIT = true in my test, and then remove it from the test when I delete the 'f' in 'fit'.

The code in the source code isn’t that bad, but in the test file I’d still like to enable the logging by adding a character or two. Also, it’d be good to have a consistent convention and tooling for this in all projects using jest.

I don’t have an exact proposal for how this should look in the source and test file. Just some ideas:

• dit instead of fit, for ‘debug-it’
• console.debug only shows up in this mode; both in the test file and source code
• process.env.JEST_FIT or similar. For code going through webpack, DefinePlugin could be used to cause DCE

Concerns:

• I would like this to work without restarting jest (e.g. no a flag/env var)
• It seems cleaner to tie this to the test file instead of a hotkey in the interactive watch mode because you want to both focus the test and enable debug logging in one operation, and then remove both in one operation.
• The code under test might call other functions that also use the debug logging mechanism

[mattphillips]

Is this something that we actually want in Jest? It seems like the problem here is trying to leave long living debugs using console.log.

This problem can be solved by using a logger that supports levels as an environment variable.

Given that we are trying to adopt: https://fishshell.com/docs/current/design.html, I’m not sure it is worth adding this to core.

I don’t think we should encourage people to add blocks of debug code to application code with Jest internals (especially if they are long living!) or to override console.debug just for tests. Both of these options will increase application code with potentially unwanted side effects, i.e. leaving a console.debug in by mistake.

Instead we should recommend using a logger with levels so that devs can confidently add logs to their code and just set the level relevant to the environment the code is being ran in.

Thoughts @SimenB @rickhanlonii?

[mackness]

Hi @SimenB, do you mind if I pick this one up?