Using jest with node assert got wrong error type.

[poppinlp]

🐛 Bug Report

The assert module in nodejs will throw error when assertion fail. It will throw a AssertionError If the second parameter is a string. But if the second parameter is an instance of Error, it will throw it instead of AssertionError.

I've tried this code and got the expected error.

const assert = require('assert');
const err = new Error('error message');

assert.ok(false, err);

But in my test case, i got an AssertionError.

To Reproduce

You may run this test case, it will fail:

const assert = require('assert');
const err = new Error('error message');

test('assert error object', () => {
  expect(() => {
    assert.ok(false, err);
  }).toThrow(err);
});

The failed error message is:

Expected behavior

Pass the test case. I know i could use something like .toThrow(err.message) to pass it, but i want to check the error type also.

Link to repl or repo (highly encouraged)

Just run the case above. :)

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: macOS 10.14.1
    CPU: (8) x64 Intel(R) Core(TM) i7-4980HQ CPU @ 2.80GHz
  Binaries:
    Node: 11.5.0 - ~/.nvm/versions/node/v11.5.0/bin/node
    npm: 6.4.1 - ~/.nvm/versions/node/v11.5.0/bin/npm
  npmPackages:
    jest: ^23.6.0 => 23.6.0

[SimenB]

This is weird. Running the snippet above behaves differently in node and through jest.

I added try-catch just to make sure jest doesn't catch the error and format it.

const assert = require('assert');
const err = new Error('error message');

try {
  assert.ok(false, err);
} catch (e) {
  console.log(e.stack);
}

Jest:

    AssertionError [ERR_ASSERTION]: Error: error message
        at Object.ok (/Users/simen/Development/jest/weird.test.js:5:10)
        at Runtime._execModule (/Users/simen/Development/jest/packages/jest-runtime/build/index.js:709:13)
        at Runtime.requireModule (/Users/simen/Development/jest/packages/jest-runtime/build/index.js:354:14)
        at /Users/simen/Development/jest/packages/jest-jasmine2/build/index.js:199:13
        at Generator.next (<anonymous>)
        at asyncGeneratorStep (/Users/simen/Development/jest/packages/jest-jasmine2/build/index.js:27:24)
        at _next (/Users/simen/Development/jest/packages/jest-jasmine2/build/index.js:47:9)
        at /Users/simen/Development/jest/packages/jest-jasmine2/build/index.js:52:7
        at new Promise (<anonymous>)
        at /Users/simen/Development/jest/packages/jest-jasmine2/build/index.js:44:12

Node:

Error: error message
    at Object.<anonymous> (/Users/simen/Development/jest/weird.test.js:2:13)
    at Module._compile (internal/modules/cjs/loader.js:688:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:699:10)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:741:12)
    at startup (internal/bootstrap/node.js:285:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:739:3)

@thymikee @rickhanlonii any ideas?

[thymikee]

IIRC we re-throw Node assert errors with custom AssertionError: https://github.com/facebook/jest/blob/master/packages/jest-circus/src/formatNodeAssertErrors.js

[SimenB]

Yeah, but that shouldn't happen when I catch it locally, unless we inject a fake assert module?

[pedrottimark]

This is a use case for us to consider when deciding on a solution for #4724

For more info about the error class see: https://nodejs.org/dist/latest-v10.x/docs/api/assert.html#assert_class_assert_assertionerror

[nicolas-van]

I confirm this behavior.

This is a burden in one of our use cases as we use assert for tasks unrelated to unit testing. Jest having unexpected side effect on the assert lib wherever it is used makes it unreliable as a unit testing framework in our case.

[adamdama]

I find it quite worrying that when I am running the code in the test environment it is being handled differently than it would in production. I should be able to rely on the fact my code will run the same in both environments otherwise the tests can't really be trusted.

[Lehks]

Are there any news on this issue? I just ran into the same problem and I'd hate to write my own assert function just to work around a longstanding bug in Jest.

[criskurtin]

Same thing here, I'm using the node's assert function to do some assertions unrelated to unit testing and this behaviour causes the custom Error class to be substituted with the AssertionError. Because of this, all custom fields get lost.

[nicolas-van]

Does anybody have a workaround for this problem ? (One that does not involve using a different assertion library in the base code)

[abiusx]

It took me 30 minutes of googling just to find this thread. Why would the library override default assert and don't even mention it anywhere in the docs?

[Westermann]

👍 Also keen on a solution here.

[ArloysMacias]

https://www.npmjs.com/package/jest-localstorage-mock

[sagi-arbroknot]

Any news on that?
It has been quite a while.

[truemoroz]

same issue

[Carl-Foster]

This is a fairly significant issue with our codebase as we use assert to handle much of our data integrity checks. The errors that are provided with the second argument also encode much of our errors messaging within the server. With Jest or Expect seemingly re-throwing the error as an AssertionError, we no longer can properly test the what is valid and quite helpful code.

[windward-hive]

thanks jest. having to do this multiple times is very convenient 👍

[Alexsey]

@maybesmurf if you are really doing this all over the project, you should consider creating your own custom matcher that will do this unwrapping for you

[tqhoughton]

posting in case anyone else stumbles on this, adding this mock to my test files fixes the issue but to other people's points it would be nice if this followed the NodeJS spec more closely.

// normally we would not need to mock nodejs internals but in this case Jest globals are incorrect
// relevant github issue: https://github.com/jestjs/jest/issues/7547
jest.mock('assert', () => ({
  __esModule: true,
  default: (statement: unknown, err: Error) => {
    if (!statement) {
      throw err
    }
  }
}))

[tqhoughton]

Checking in on this thread I ended up completely abandoning trying to mock assert "correctly" since many other libraries use assert under the hood and depending on which order you are mocking things and importing libraries you can easily end up in a state where a third party library calls your own custom assert mock and breaks things due to it not being 100% correct.

This is an unfortunate case where the easiest solution is to use a third party module instead of node built-ins due to how Jest decides to override node defaults.