Bug: An error occurs when invoking ESLint#lintFiles() in Jest

[NobleMathews]

Environment

Node version: 20.12.2 npm version: 10.5.0 Local ESLint version: 9.1.1 Global ESLint version: 9.1.1 Operating System: macOS

What parser are you using?

Default (Espree)

What did you do?

Configuration

``` 'use strict' module.exports = [ { languageOptions: { parserOptions: { ecmaVersion: 'latest', }, }, ignores: [ '**/node_modules/**', ], rules: { indent: ['error', 2], quotes: ['error', 'single'], semi: ['error', 'never'], }, }, ] ```

• Actual code

'use strict'

const {
  ESLint,
} = require('eslint')

describe('ESLint Bug', () => {
  test('should not throw an error', async () => {
    const eslint = new ESLint()
    const filePaths = [
      'tests/resources',
    ]
    const expectedLength = 3

    const results = await eslint.lintFiles(filePaths)

    expect(results)
      .toHaveLength(expectedLength)
  })
})

• Test Resources

tests/resources/indent.js

'use strict'

module.exports = function doubleValue ( value, ignore ) { if (ignore) { return value }

return value + value } tests/resources/quotes.js

'use strict'

module.exports = "quotes" tests/resources/semi.js

'use strict'

global.semi = 111;

What did you expect to happen?

I expect that Jest shows the log below

PASS tests/tests/eslint-bug.js ESLint Bug ✓ should not throw an error (121 ms)

Test Suites: 1 passed, 1 total Tests: 1 passed, 1 total Snapshots: 0 total Time: 1.221 s, estimated 2 s Ran all test suites.

What actually happened?

An error Result is not a promise. is thrown.

FAIL tests/tests/eslint-bug.js ESLint Bug ✕ should not throw an error (105 ms)

● ESLint Bug › should not throw an error

Result is not a promise.

  13 |     const expectedLength = 3
  14 |
> 15 |     const results = await eslint.lintFiles(filePaths)
     |                     ^
  16 |
  17 |     expect(results)
  18 |       .toHaveLength(expectedLength)

  at Retrier.retry (node_modules/@humanwhocodes/retry/dist/retrier.cjs:200:35)
      at Array.map (<anonymous>)
  at Object.<anonymous> (tests/__tests__/eslint-bug.js:15:21)

Test Suites: 1 failed, 1 total Tests: 1 failed, 1 total Snapshots: 0 total Time: 1.195 s Ran all test suites.

Link to Minimal Reproducible Example

-

Participation

• [ ] I am willing to submit a pull request for this issue.

Additional comments

No response

[mayil-ai[bot]]

Doesn't seem like we have fully grasped all the specifics of this ticket. But here are some ideas that might help you get started:

To address the error "Result is not a promise." when invoking ESLint#lintFiles() within a Jest test, perform the following actions:

• Verify that your Jest test environment is properly configured to handle asynchronous operations. This includes checking for proper usage of async/await in your test functions.
• Confirm that the version of ESLint you are using in your project is the one that supports the lintFiles() method returning a promise. You may need to check the ESLint documentation or the package.json file to ensure compatibility.
• If the problem continues, implement additional logging within the test to trace the execution flow. You can add console.log statements before and after the lintFiles() call to verify the behavior:

  console.log('Before lintFiles call');
  const result = await eslint.lintFiles(patterns);
  console.log('After lintFiles call', result);

• Alternatively, use a debugging tool to step through the code. Place a breakpoint at the lintFiles() invocation to inspect the returned value and determine why it is not recognized as a promise. This can help identify where the promise is being mishandled.

Code snippets to check

• lib/eslint/legacy-eslint.js:530-640 | Contains 'lintFiles' method which may need to be edited to return a promise and resolve the 'Result is not a promise' error.

• lib/linter/linter.js:1-69 | Provides context for the main Linter class which could be relevant for understanding the issue with 'lintFiles' method.

• lib/eslint/eslint.js:578-578 | Mentions the ESLint class which is instantiated in the issue description, may need review for constructor or initialization issues.