New Rule: require-test-suggestions

[bmish]

It would require invalid test cases to assert what suggestions are provided for each violation (using suggestions: [] if the violation provides no assertions).

Why?

• Currently, it's easy to forget to assert what suggestions a test case yields, or that a test case yields no assertions. As a result, this can be an area of poor test coverage.

new RuleTester().run('example-rule', rule, {
  valid: [],
  invalid: [
    {
      code: `foo();`,
      output: null,
      errors: [
        {
          messageId: 'bar',
          type: 'Property',
          suggestions: [], // or array of suggestions if rule offers them
        },
      ],
    },
  ]
});

This rule would have a consistent option (enabled by default), which would only require the suggestions assertion if at least one test case in the file has it (similar to eslint-plugin/consistent-output).

I hope that a future major version of ESLint will require test cases that yield suggestions to assert what they are, so that this lint rule wouldn't be as necessary as it is now. Here is the issue I file about this: eslint/eslint#15104

[bmish]

Closing because I plan to pursue an improvement in ESLint v9 (eslint/eslint#15104) that will result in this rule being no longer needed.