模块中的单元测试功能

Question

Ok, I'm making a serious stab at learning about unit testing for the first time, I'm using Mocha & Sinon.

So hypothetical dumb module, contains functions foo and bar . Foo depends on bar .

(function() {

  var bar = function(callback) {
    if (willOfTheGods) {
      callback('err', null);
    } else
      callback(null, 'hurrah');
  }

  var foo = function() {

    bar(function(err, res) {
      //blah deh blah
    });
  }

  module.exports = {
    bar: bar,
    foo: foo
  }

})();

I want to stub bar so I can test foo .

This seems logical from the Sinon docs ...

var myModule = require('../myModule');
sinon.stub(myModule, 'bar')
myModule.bar.callsArgWith(0, ['err', null]);

but it only works if I call bar in the test itself.

myModule.bar(function(err, result){
  console.log('err, result');
});

When I call myModule.foo it still uses the original 'unstubbed one'.

It seems like creating a stub just creates a new local variable for that function rather than stubbing it in the module.

Or am I missing something completely - or just doing the wrong thing?

Answer 1

Ok, Some research revealed that stubbing like this is only replacing the value of the module.exports property not the underlying function. So I need to use something like rewire to actually get inside the module.

So now if I drop the Sinon stub and just do:

var myModule = rewire('../myModule');

myModule.__set__('bar', function(callback){
  callback('err', null);
});

it works ... kind of. It only works if I remove the self executing function wrapping from myModule, ie remove (function(){ ... })(); . My understanding was that was a best-practice ... but maybe only in the browser? Whole different question there I guess.