hajest-my-error.js

import assert from 'assert';
import {assertThat, instanceOf, throws} from 'hamjest';

class MyError extends Error {
  constructor(...args) {
    super(...args);
  }
}

function throwingFunction() {
  throw new MyError();
}

describe('catch my error', () => {

  it('finds error', () => {
    assertThat(throwingFunction, throws(instanceOf(MyError)));
  });

});

the output when running the tests

  catch my error
    1) finds error


  0 passing (494ms)
  1 failing

  1) catch my error finds error:

Expected: a function throwing an instance of MyError
     but: thrown object: {"stack":"Error\n    at MyError.Error (native)\n    at new MyError (test.js:4:7)\n    at throwingFunction (test.js:11:9)\n    at Object.IsFunctionThrowing._.create.describeMismatch (/Users/cain/programming/tmp/hamjest-testing/node_modules/hamjest/lib/matchers/IsFunctionThrowing.js:28:5)\n    at assertThat (/Users/cain/programming/tmp/hamjest-testing/node_modules/hamjest/lib/assertThat.js:28:11)\n    at Context.<anonymous> (test.js:17:5)\n    at callFn (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runnable.js:315:21)\n    at Test.Runnable.run (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runnable.js:308:7)\n    at Runner.runTest (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:422:10)\n    at /Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:533:12\n    at next (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:342:14)\n    at /Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:352:7\n    at next (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:284:14)\n    at Immediate._onImmediate (/Users/cain/programming/tmp/hamjest-testing/node_modules/mocha/lib/runner.js:320:5)\n    at processImmediate [as _immediateCallback] (timers.js:368:17)"} is a Error
  AssertionError: 
  Expected: a function throwing an instance of MyError
      at Context.<anonymous> (test.js:17:5)

I would have expected the test to pass, because throwingFunction does throw MyError, but the tests fails :(

Interesting… your code seems correct.
Can you open a ticket with more details about your environment, please? We can investigate it there.

Must be the ES6 class syntax. Seems like new MyError() instanceOf MyError is falsy — odd.