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)));
  });

});

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