Am I using Q the right way or is there a better way to do what I'm doing?

Question

I'm using Q to flatten out some callbacks in my unit tests and return a promise to mocha (which knows to wait until the promise is resolved before running the next test).

Originally I had this code:

it ('resetCount should cause the count to reset as if there were no documents yet.', function () {
    // Now save user and check if its _id is what nextCount said.
    user.save(function (err) {
        should.not.exists(err);
        user._id.should.eql(0);

        // Call nextCount to check the next number. Should be one.
        user.nextCount(function (err, count) {
            should.not.exists(err);
            count.should.eql(1);

            // Now reset the count.
            user.resetCount(function () {
                // Call nextCount again to check that the next count is reset. Should be zero.
                user.nextCount(function (err, count) {
                    should.not.exists(err);
                    count.should.eql(0);
                    done();
                });
            });
        });
    });
});

With Q I turned it into this:

it('resetCount should cause the count to reset as if there were no documents yet.', function () {
    var userSchema = new mongoose.Schema({
        name: String,
        dept: String
    });
    userSchema.plugin(autoIncrement.plugin, 'User');
    var User = db.model('User', userSchema);

    // Create user and save it.
    var user = new User({name: 'Charlie', dept: 'Support'});
    // Now save user and check if its _id is what nextCount said.
    q.nmcall(user, 'save')
        .then(function (user) {
            user._id.should.eql(0);
            return q.nmcall(user, 'nextCount');
        })
        .then(function (count) {
            count.should.eql(1);
            return q.nmcall(user, 'resetCount');
        })
        .then(q.nmcall(user, 'nextCount'))
        .then(function (count) {
            count.should.eql(0);
        }, function (err) {
            should.not.exists(err);
        });

});

I no longer have to call the done callback because of how mocha understands to wait for the promise to resolve. I am new to Q so I'm wondering if I've done things the most efficient way. It seemed like calling node-style mongoose methods with q.nmcall (alias for q.invoke) made the most sense. However, if you think you could write the same code better then please let me know where I can improve it.

Answer 1

.then(q.nmcall(user, 'nextCount'))

is wrong. The nextCount call does return a promise (and starts its execution right away), while then does expect a [callback] function. You'd rewrite it to

.then(function(result_of_resetcount) {
    return q.nmcall(user, 'nextCount');
})

or shorten it with nfbind/nbind:

.then(q.nbind(user.nextCount, user))