Refactoring Test Helper Methods with Talents

talents node javascript
July 24, 2013

We consider tests mandatory in CocktailJS repository, not only unit tests but integration tests as well. And with those tests we found ourselves having to create some test helper methods to create some possible scenarios and restore state for example. We added some comments in lib/cocktail.js file as a friendly reminder that those methods should go away when we find a better design or strategy.

    // -- >Experimental

    // --- This methods are used for testing, find a better desing to avoid them

    restoreDefaultProcessors: function() {
        var key,
            DEFAULT_PROCESSORS = cocktail._DEFAULT_PROCESSORS;

        this.setProcessors({});

        for(key in DEFAULT_PROCESSORS){
            if(DEFAULT_PROCESSORS.hasOwnProperty(key)) {
                this._processors[key] = DEFAULT_PROCESSORS[key];
            }
        }

    },

    clearProcessors: function() {
        var processors = this.getProcessors(),
            key;
        for(key in processors){
            if(processors.hasOwnProperty(key) && key !== 'no-op'){
                delete processors[key];
            }
        }
    },

    // -- >End of Experimental

Talents

So, what we can do to remove those methods from the code? Talents was the response. A Talent is a special case of class where we define only behavior and they cannot contain any state making the mix safer (There are other rules as well that prevent to override existing methods).

Refactoring with Talents

We were using the restoreDefaultProcessors method in our tests so we needed to extract the method in a Talent that we named RestoreProcessor - since it is a Talent, it is not necessary to name it as a noun, after all it should describe which behavior is provided by the Talent.

We mentioned that our Talent will be used only as a Test Helper, so it won't be shipped as part of the library. That being said, the Talent was placed into our test/helper folder.

test/helper/RestoreProcessor.js

var cocktail = require('../../lib/cocktail');

cocktail.mix({
    '@exports': module,

    restoreDefaultProcessors: function () {
        //TODO ... 
    }
});

Now we need to declare what methods will be required to be defined in the object where we are going to add the Talent. Our Talent cannot define any state, so we need to specify how we can access the state using the @requires annotation. In this case, we need access to the default processor list and the current processors in order to restore them.

test/helper/RestoreProcessor.js

var cocktail = require('../../lib/cocktail');

cocktail.mix({
    '@exports': module,

    '@requires': [
        'setProcessors',
        'getDefaultProcessors'
    ],

    restoreDefaultProcessors: function () {
        //TODO ... 
    }
});

After defining the required methods, we can now start to refactor our method inside the Talent:

test/helper/RestoreProcessor.js

var cocktail = require('../../lib/cocktail');

cocktail.mix({
    '@exports': module,

    '@requires': [
        'setProcessors',
        'getDefaultProcessors'
    ],

    restoreDefaultProcessors: function () {
        var key,
            defaultProcessors = this.getDefaultProcessors(),
            processors = {};

        for(key in defaultProcessors){
            if(defaultProcessors.hasOwnProperty(key)) {
                processors[key] = defaultProcessors[key];
            }
        }

        this.setProcessors(processors);

    }
});

Almost done! The Talent is defined already and we have to apply it to the cocktail instance in our test. We need to require the Talent and apply it.

test/integration/cocktail.js

//...

var chai = require("chai"),
    //...
    cocktail = require('../../lib/cocktail'),
    RestoreProcessors = require('../helper/RestoreProcessors');

    //...
    cocktail.mix(cocktail, {
        '@talents': [RestoreProcessors]
    });

    //...

     afterEach(function(){
        cocktail.restoreDefaultProcessors();
    });

    //...

One last step before we run our code is to remove the current definition in lib/cocktail.js file first because we don't need it anymore, and more importantly because it will fail if we apply a Talent with a method definition that is overriding an existing method in the target object.

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