Javascript Testing Basics: Update jest globals/ESLint setup info

[ToastedGMS]

Because

This PR adds a short paragraph with information regarding Jest global imports when working with ESLint.

This PR

• Adds a short paragraph pointing to the Jest docs, explaining Jest setup with ESLint.

Issue

Closes #29509

Additional Information

Link to issue discussion

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[mao-sz]

Thanks - I know the below was my original suggestion but on another read, I think some people may wonder where the link to the Getting Started tutorial is, and I don't think we need to link the page twice. What do you think of the below instead?

Suggested change

1. Follow along to Jest’s Getting Started tutorial. For the upcoming testing practice and project, you only need to follow the instructions for installing Jest. Note that while Jest includes global variables like `test` and `expect`, if you are using ESLint, you'll still want to [import the Jest globals your test file needs](https://jestjs.io/docs/getting-started#using-eslint) so ESLint doesn't complain about them.

1. Follow along to [Jest's Getting Started tutorial](https://jestjs.io/docs/getting-started) until you reach the "Additional Configuration" section, then read the "Using ESLint" section regarding ESLint and Jest globals like `test` and `expect`.

[ToastedGMS]

I think it works to point the reader in the direction of the resource's info, but doesn't explicitly state the Jest globals information, which may leave the reader hanging regarding whether or not to import them, like the original issue was. In my opinion it boils down to how detailed we want to make this and linking to your original comment, having learners go out of scope on their own terms if they wish to do so. Maybe we could sum it up as

Follow along with Jest’s Getting Started tutorial up to the "Additional Configuration" section—only the installation steps are needed for the upcoming testing practice and project. Jest provides global variables like test and expect, but if you're using ESLint, you'll need to explicitly import these in your test files to prevent linting errors (see the "Using ESLint" section in the same tutorial).

[mao-sz]

I like the latter half of your wording. Just mixing in my former half because just saying "the installation steps" isn't actually quite clear enough which sections are included and excluded (e.g. the Babel stuff, which is linked in a later lesson when relevant).

Suggested change

1. Follow along to Jest’s Getting Started tutorial. For the upcoming testing practice and project, you only need to follow the instructions for installing Jest. Note that while Jest includes global variables like `test` and `expect`, if you are using ESLint, you'll still want to [import the Jest globals your test file needs](https://jestjs.io/docs/getting-started#using-eslint) so ESLint doesn't complain about them.

1. Follow along to [Jest's Getting Started tutorial](https://jestjs.io/docs/getting-started) until you reach the "Additional Configuration" section. Jest also provides global variables like `test` and `expect`, but if you're using ESLint, you'll need to explicitly import these in your test files to prevent linting errors (see the "Using ESLint" section in the same tutorial).