Unexpected throw in `.throws()`

[StoneCypher]

You can replicate by pulling my repo and uncommenting the commented-out test.

Test Source

  it('probable exits for throws on non-state', t => t.throws(() => {
    const machine = new jssm.machine({
      initial_state: '1',
      transitions:[
        { name:'id1', from:'1', to:'2', action:'identical' }
      ]
    });
    // why does this test fail Threw unexpected exception: 'No such state "3" in probable_exits_for' >:(
    machine.probable_exits_for('3');
  }, Error));

Error Message & Stack Trace

  general › Illegal machines probable exits for throws on non-state
  /Users/johnhaugeland/projects/jssm/src/js/tests/general.js:780

   779:                                                                     
   780:   it('probable exits for throws on non-state', t => t.throws(() => {
   781:                                                                     

  Threw unexpected exception:

  'No such state "3" in probable_exits_for'

The exception is expected, and that is the correct exception message.

This test is a .throws(). I don't understand why this is treated as a failure. Near-verbatim identical tests cover my other throws and work as expected.

Config

I do not configure Ava. No such block or .rc exists in my project.

Command-Line Arguments

My build is trivial.

    "test": "ava src/js/tests/*.js",

Relevant Links

This is the repo.

Environment

Replicates under MacOS current and Windows 10 Pro current. Both tested under node 8 current.

Replicates on travis-ci under node-6, node-7, and node-8, all current, all under whatever linux they use.

All are using ava 0.20.0, installed as local node modules.

[sindresorhus]

You're throwing a string and not an Error object: https://github.com/StoneCypher/jssm/blob/6f22cc476a2a24476a10f6d5c8f75bead619f48e/src/js/jssm.js#L265

[StoneCypher]

Oh.

May I please recommend that the error message here point that out as a possibility? It would not have occurred to me that throwing a string wouldn't be caught by .throws .

[StoneCypher]

And/or should strings thrown be caught by .throws ?

[kevva]

You should use throw new Error(string) in your code. Read more about the Error object here https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Error#Throwing_a_generic_error.

[StoneCypher]

@kevva - sorry, no, throw can and always has legally accepted strings, as the first example on your source shows.

[kevva]

I'm aware of that, but it's a bad practice.

And/or should strings thrown be caught by .throws ?

There has been some discussion around it in #661 and a new proposal for throws in #1047.

Will close this as a duplicate.

[StoneCypher]

this is not a duplicate of 661; the behavior is entirely different, and does not appear to be defective in presentation

this is not a duplicate of 1047, which is about simplifying throws, and barely touches on this in passing

i wish this had not been closed, and generally it's polite to ask the person opening the ticket before closing

i retain the belief that throws should accept all valid throws, which it currently does not, without mentioning that in the documentation

[sindresorhus]

@StoneCypher It's because you specified it to expect an Error object in the assertion, but you threw a string. I've opened #1440 instead to improve the experience.

[StoneCypher]

Thank you.