Make `-u` option more user friendly and less error-prone

🚀 Feature Proposal

Basically after seeing this interactive snapshot updater I think it would make sense if the -u option were to show a prompt to update snapshots similar to running in interactive mode.

Additionally I would propose a -U (or other unused flag) to be equal to the current behavior

Motivation

I think snapshot testing is awesome! But I’ve been having a hard time convincing a coworker and he’s got a valid point about the -u option, it’s entirely too easy to update all the snapshots and let stuff slip in. If the -u option were to use the interactive prompts for updating with diff views and the -U option were to clearly state it’s an “unsafe” option and do a y/n confirm I think it’d make the user experience around snapshot testing more explicit.

Pitch

The core Jest experience shouldn’t make it easy to shoot yourself in the foot like the current -u option does.

[thymikee]

I think it actually makes sense to make updating all the snapshots a bit harder, especially that we now can update snapshots one by one, but only in watch mode. We just need to figure out the best way to do it. How about this flow:

1. [watch mode] Press u
2. Jest prompts:

You're about to update *all* snapshots
> Press `u` or `y` to continue
> Press `n` or `esc` to abort
> Press `i` to update snapshots interactively

I think it’s nice to be able to continue by pressing u once more, just not be too annoying.

[rickhanlonii]

I guess I don’t really see this as a foot-gun if you’re following best practices