jest --coverage fails while jest passes

🐛 Bug Report

When using coverage with jest, the toString method of the child class is lost.

To Reproduce

Create and error class with it’s own toString method.

  export default class ExampleError extends Error {
    constructor(status, statusText, url, headers, response) {
          super('test message');
      }
  
      toString() {
          return `replacement serialization`;
      }
  }

Try testing the above file.

import ExampleError from './ExampleError';
  
describe('ExampleError', () => {
    it('throws the error with the properties attached', () => {
        const error = new ExampleError();

        expect(String(error)).toEqual('replacement serialization');
    });
});

Use this jest config (thought it probably isn’t really required)

module.exports = {
    verbose: true,
    testURL: 'http://localhost',
};

Test just running jest with no values.

project $ ./node_modules/.bin/jest 
 PASS  src/ExampleError.test.js
  ExampleError
    ✓ throws the error with the properties attached (4ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.799s, estimated 1s
Ran all test suites.

Try running with coverage.

project $ ./node_modules/.bin/jest --coverage
 FAIL  src/ExampleError.test.js
  ExampleError
    ✕ throws the error with the properties attached (10ms)

  ● ExampleError › throws the error with the properties attached

    expect(received).toEqual(expected)

    Expected value to equal:
      "replacement serialization"
    Received:
      "Error: test message"

       5 |         const error = new ExampleError();
       6 | 
    >  7 |         expect(String(error)).toEqual('replacement serialization');
         |                               ^
       8 |     });
       9 | });
      10 | 

      at Object.<anonymous> (src/ExampleError.test.js:7:31)

-----------------|----------|----------|----------|----------|-------------------|
File             |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------------|----------|----------|----------|----------|-------------------|
All files        |       50 |      100 |       50 |       50 |                   |
 ExampleError.js |       50 |      100 |       50 |       50 |                 7 |
-----------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        1.044s
Ran all test suites.

Expected behavior

I expect both jest and jest --coverage to output similar results.

Run npx envinfo --preset jest

Paste the results here:

npx envinfo --preset jest
npx: installed 1 in 1.958s

  System:
    OS: macOS High Sierra 10.13.6
    CPU: x64 Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
  Binaries:
    Node: 10.8.0 - /usr/local/bin/node
    Yarn: 1.9.4 - /usr/local/bin/yarn
    npm: 6.2.0 - /usr/local/bin/npm
  npmPackages:
    jest: ^23.4.2 => 23.4.2 

[alberthuynh91]

Ran into an issue with the antd Select component. Jest errors with ReferenceError: Select is not defined when running test runner with --coverage flag jest --coverage but all my tests pass fine when I run jest without the flag. Does anyone know how I could fix this? Been googling around with no luck.

---

Edit (update): Turns out I was trying to destructure const { Option } = Select and when I refactored to use dot notation <Select.Option> the error was no longer throwing. Very weird that this only happens on jest --coverage and not on jest.

[mydiemho]

@rickhanlonii can you explain why you believe this is not a Jest issue?

I am seeing the same thing and I’m not using Istanbul. I believe this is a Jest issue because regardless of what is used, jest and jest --coverage should produce similar results.