testing should.throw() on asynchronous code

[jmarca]

I am trying to test that an async bit of code should throw an error, but should.throw() doesn't seem set up for async code.

For example

 (function(){ 
    fs.readFile('fake.file', function (err, data) {
      if (err) throw err;
    });
  ).should.throwError();

That doesn't work.

Should one instead attach a listener on the process' uncaught exception handler?

it('should throw',function(done){
  process.on('uncaughtException', function(err) {
    console.log('Caught exception: ' + err);
    return done();
  });
  fs.readFile('fake.file', function (err, data) {
    if (err) throw err;
  });
  return null; 
})

Of course, that doesn't work either (I get Caught exception: Error: ENOENT, open 'fake.file'), but somehow the done() is skipped and the test fails with

 1) verify config checker should throw:
     Uncaught Error: ENOENT, open 'fake.file'

and anyway, the node.js docs deprecate uncaughtException in favor of domains, which I haven't learned yet.

Guidance or a new feature would be appreciated.

[btd]

Maybe something like this?

fs.readFile('fake.file', function (err, data) {
     err.should.be.Error; //it is in case you are sure it will be, it will fail on null with standard message that null it is not an object or similar
should(err).be.Error; // in case you are not sure it will fail if no error with more descriptive message
    });

.throw created only for sync functions, for async flow usually you need to make test inside callback.

[jmarca]

Well, the "readFile" was a toy example, just trying to get something that throws an error, not reports an error in the err argument. The function I am testing does a stat on a file and (originally) would throw if the file was not mode '0600'.

When the function calls throw(), the callback is not triggered. I was hoping to hack something based on should.throw(), but you confirmed it isn't possible.

I'll dig into domains and try to solve this properly

[btd]

If you need to be sure that callback called then you better to add sinon, spy will check if function was called.