add helper function to execute test and only fire callback once

[inssein]

Fixes #645

[LinusU]

I don't understand, how does this make sure that callbacks only fire once? Could you please explain your code :)

[inssein]

@LinusU I just wrote a simple test, and ran it across 4 different versions of node. Looks like it never worked, or I am missing something.

var done = function() {
  console.log('done');
};

var fn = function(ctx, done) {
  done();
};

2 == fn.length ? fn('test', done) : fn('test'), done();

The above code will print done twice. Once by going through fn(), and once by being called at the end of the last line. This breaks the test for me as /jpeg and /render will try to send the result twice.

[LinusU]

Cool, yes I have seen this behaviour as well actually

[inssein]

@LinusU what's the process on getting this merged?

[LinusU]

Merging now, sorry for the delay

[inssein]

@LinusU thanks!

[LinusU]

Thank you, help is always appreciated!