tests: migrate to FlatRuleTester v8

[MikeMcC399]

Issue

Tests in the tests/lib/rules directory which run internally under ESLint 8.x are not compatible with ESLint 9.x.

The guide Migrate to 9.0 > FlatRuleTester is now RuleTester explain:

As announced in our blog post, the temporary FlatRuleTester class has been renamed to RuleTester, while the RuleTester class from v8.x has been removed. Additionally, the FlatRuleTester export from eslint/use-at-your-own-risk has been removed.

This is a breaking change for the tests.

Migration steps

The migration is done in two steps:

1. Migrate to the temporary FlatRuleTester class in ESLint 8.x
2. Migrate to the new RuleTester class in ESLint 9.x and at the same time migrate to using ESLint 9.x internally.

Changes

This PR deals with the first step of migrating to the temporary FlatRuleTester class in ESLint 8.x.

A follow-on PR will take care of the second step of migrating to ESLint 9.x

For all tests/lib/rules *.js test files

1. Use const { FlatRuleTester } = require('eslint/use-at-your-own-risk') according to the blog post Testing rules with flat config and the RuleTester class.
2. Change parserOptions to languageOptions.
3. For tests/lib/rules/no-unnecessary-waiting.js remove the section which attempts to test disabling the rule. This is not compatible with the FlatRuleTester and it is attempting to test a function of ESLint rather than the rule itself.
4. For tests/lib/rules/unsafe-to-chain-command.js modify an incompatible option syntax in one rule.

References

• Testing rules with flat config and the RuleTester class
• FlatRuleTester is now RuleTester
• v9 > RuleTester

Verification

Ubuntu 22.04.4 LTS, Node.js v20.12.2 LTS

npm ci
npm run test

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[MikeMcC399]

It is not possible to have one set of tests which can be used on v7, v8 and v9, so the proposed migration strategy will not work.

Closing this PR as a different approach is needed here.

[MikeMcC399]

• Superseded by PR tests: save legacy tests #205