Jest: Allow console.error/warn/log to be overwritten in tests

Created on 31 Mar 2017 · 3Comments · Source: facebook/jest

Do you want to request a feature or report a bug?
feature

What is the current behavior?
Due to the BufferedConsole, it's impossible to overwrite console.error, console.log, console.warn and console.info.

Use Case: We'd like to be able to have console.error and console.warn throw errors and fail tests.

If the current behavior is a bug, please provide the steps to reproduce and either a repl.it demo through https://repl.it/languages/jest or a minimal repository on GitHub that we can yarn install and yarn test.

What is the expected behavior?
I expect that if I add console.error = (message) => { throw new Error(message); }; (globally, in a test, or in setupFiles/setupFramework), that any time console.error is called in a test it would throw an error and fail a test.

In reality, nothing happens.

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

N/A

Source

paularmstrong

Most helpful comment

Use mocking function jest.fn():

console.warn = jest.fn(warn => {
  throw new Error(warn);
});

thymikee on 1 Apr 2017

👍3

All 3 comments

Use mocking function jest.fn():

console.warn = jest.fn(warn => {
  throw new Error(warn);
});

thymikee on 1 Apr 2017

👍3

@thymikee This isn't working as expected either, using a global setup file:

in "setupTestFrameworkScriptFile": "<rootDir>/tools/jest/setup-framework.js"

beforeEach(() => {
  console.error = jest.fn((error) => {
    throw new Error(error);
  });
});

In test:

const somePromiseThatLogsConsoleError = () => {
  return new Promise((resolve, reject) => {
    console.error('foobar');
    resolve();
  });
});

it('test that has console.error', () => {
  return somePromiseThatLogsConsoleError().then(() => {
    expect(false).toBeTrue();
  });
});

paularmstrong on 3 Apr 2017

i just tried it and it worked:

// test file
test('lol', () => {
  return new Promise((resolve) => {
    console.log('lol');
    resolve();
  });
});

// setup file
global.console.log = () => {
  throw new Error('hey!');
};

result:

 __tests__/test-test.js
  ✕ lol (3ms)

  ● lol

    hey!

      at CustomConsole.Object.<anonymous>.global.console.log (setup.js:2:9)
      at resolve (__tests__/test-test.js:3:13)
      at Object.<anonymous>.test (__tests__/test-test.js:2:10)
      at process._tickCallback (internal/process/next_tick.js:109:7)

Test Summary
 › Ran all tests.
 › 1 test failed, 0 tests passed (1 total in 1 test suite, run time 0.661s)