The `unhandledRejection` handler is not testable anymore.

[despairblue]

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

Regression

What is the current behavior?

Current versions of jest don't allow testing unhandledRejections. The following test will never succeed:

const foo = require(".");

describe("foo", () => {
  test("bar", done => {
    process.removeAllListeners("unhandledRejection");
    process.on("unhandledRejection", function(error) {
      process.removeAllListeners("unhandledRejection");
      expect(error).toBeInstanceOf(Error);
      done();
    });

    foo();
  });
});

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.

I made a repository with two commits with different jest versions showing that it works with an older version but not anymore with the current one. The README describes the repro steps in detail.

What is the expected behavior?

It should be possible to test unhandledRejection and uncaughtExceptions.

Btw I'm well aware that this is a case of https://xkcd.com/1172/ and that we could refactor the code to not rely on unhandledRejection for error reporting of unknown errors that happen. But it's actually really convenient to use the unhandledRejection handler to report to rollbar and shutdown the process orderly.

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

OS: Mac 10.12.6
Node: v8.9.4
Yarn: 1.3.2

[JeffBaumgardt]

Not to dredge up the dead but I have a similar issue with testing unhandledrejection. Consider

window.addEventListener('unhandledrejection', event => this.onUnhandledRejection(event), {
    passive: true,
})

This code should take any unhandled promise rejection and work with it.

It works in browser but I think jsdom or jest doesn't support it. For now I have the line ignored but it would be nice to have.

OS: Windows 10
Node: 10.7.0
NPM: 6.0.0

[LukasBombach]

Confirming the bug with a simple example:

test('catches unhandled rejections', async () => {
  const errorHandler = jest.fn();
  const error = new Error('mock error');
  process.on('unhandledRejection', err => errorHandler(err))
  await Promise.reject(error);
  expect(errorHandler).toHaveBeenCalledWith(error);
});

will give you this

● catches unhandled rejections

mock error

  13 |
  14 | test('catches unhandled rejections', async () => {
> 15 |   const error = new Error('mock error');
     |                 ^
  16 |   const errorHandler = jest.fn();
  17 |   process.on('unhandledRejection', err => errorHandler(err))
  18 |   await Promise.reject(error);

  at Object.<anonymous>.test (test/bin.test.js:15:17)

OS: macOs 10.13.6
Node: v8.11.4 (LTS)
Yarn: 1.9.4

I also took this to StackOverflow: https://stackoverflow.com/questions/52493145/how-to-test-a-unhandledrejection-uncaughtexception-handler-with-jest

[kschat]

Has anyone found a workaround for this issue?

[wearhere]

Confirmed that this breaks testing functions that throw uncaught exceptions, too: https://repl.it/repls/FreeFluffyAdministration

[sb-junhyeong]

This should be resolved because unhandledPromiseRejection might make random subsequent test fail.

[deepal]

Any update on this issue yet?

[jrnail23]

Same problem here... trying to test my error handling (logging, Sentry reporting). It works fine in my other app that uses mocha for its tests, but Jest just won't let me do it.

[sadokmtir]

+1

[curiosity26]

+1