`TypeError: Cannot read property 'concat' of undefined` when running ESLint via Jest

This error occurs when running ESLint from a Jest test:

TypeError: Cannot read property 'concat' of undefined
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/eslint/lib/util/module-resolver.js:28:30)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/eslint/lib/config/config-file.js:23:22)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/eslint/lib/config.js:17:18)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/eslint/lib/cli-engine.js:31:14)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/eslint/lib/api.js:10:16)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/src/index.js:1:136)
    at Object.<anonymous> (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/src/__tests__/index-test.js:3:12)
    at jasmine2 (/Users/spencerelliott/Sites/elliottsj/eslint-jest-issue-5791/node_modules/jest-jasmine2/src/index.js:154:16)

What version of ESLint are you using? eslint@2.7.0

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration: https://github.com/elliottsj/eslint-jest-issue-5791/blob/master/.eslintrc

{
  "extends": "eslint:recommended",
  "env": {
    "jest": true,
    "node": true
  }
}

What did you do? Please include the actual source code causing the issue.

See the full example here: https://github.com/elliottsj/eslint-jest-issue-5791

// index.js
var CLIEngine = require('eslint').CLIEngine;

function lint() {
  var cli = new CLIEngine();

  // Lint this file
  var report = cli.executeOnFiles(['index.js']);

  return report;
}

module.exports = {
  lint: lint
};

// __tests__/index-test.js
jest.unmock('..');

var lint = require('..').lint;

describe('eslint CLIEngine', function() {
  it('should work with Jest\'s module system', function() {
    var report = lint();
    expect(report.results).toBeDefined();
  });
});

What did you expect to happen?

Expected the Jest test to pass without error.

What actually happened? Please include the actual, raw output from ESLint.

See error shown above.

---

ESLint v2.5.3 runs fine: https://github.com/elliottsj/eslint-jest-issue-5791/tree/eslint-2.5

It seems the issue was introduced as a result of https://github.com/eslint/eslint/commit/4ecd45e549c8622a26f5b105dd43b7a2827cf942: here is the failing line: https://github.com/eslint/eslint/commit/4ecd45e549c8622a26f5b105dd43b7a2827cf942#diff-6535c964600bdcc5abbfefe8282e96f3R28

[cpojer]

This was fixed in Jest 11.0.

[cpojer]

@nzakas Is there a reason why eslint is using module.paths at all? It seems like it is undocumented private API that is an implementation detail of the node module resolution algorithm.

Jest sandboxes all JavaScript code for proper test isolation (that way no module or test can impact another test). We are using node-resolve for all resolution which has a userland implementation of what module.paths gives you. I suggest to use it instead: https://github.com/substack/node-resolve