CODEWITHSUNDEEP
unit-testing
Levi Hackwith
Levi Hackwith

Reputation: 9332

Should I Write Unit Tests That Check the Default Values of An Object's Properties?

The question title really says everything, but I'll do my best to clarify things. Let's say I have the following object:

function MyObject() {
    this.isAwesome = true;
    // Other methods and property
}
var obj = new MyObject();

Now, when writing unit tests against this object, should I write a test that makes sure that the isAwesome property defaults to true? Or is that too rigid of a test?

Upvotes: 1

Views: 2525

Answers (3)

2rs2ts
2rs2ts

Reputation: 11026

It depends on whether the constructor is capable of changing that default value. I don't know what language this is you're writing, so I'll just wing it:

function MyObject(stopBeingAwesome) {
    this.isAwesome = true;
    if (stopBeingAwesome) {
        this.isAwesome = false;
    }
}

If this is the case, then you can test that logic. Otherwise, you're unit testing a basic language construct such as assignment.

Unit tests are supposed to test the contracts of a unit of code. That is, the same input should always result in the same output. In this case, your contract involves this.isAwesome being true when the object is finished being constructed. However, unless someone changes the implementation of MyObject so that isAwesome won't be true, it's not necessary to test that. And, if someone does change the implementation, they'll have to modify the test too. Worrying about regression at this level means that you're afraid that your other tests won't successfully test the default behavior, and that your coworkers are code saboteurs who will gleefully modify your constructor's default behavior for no apparent reason without telling you and without running your integration test suite.

It may seem like I am against regression tests, but when a build takes 20 minutes on Jenkins, you start to be grateful that you decided not to test some things.

Upvotes: 1

Damien Black
Damien Black

Reputation: 5647

Only write the test if the variable isAwesome is somehow part of the public facing portion of the class. If isAwesome just affects the behaviour of the class, test instead for that behavior.

Typically, a variable like that should not be part of the public facing portion of the class. For clean code, the least that would be required is that the variable be private and have getter and setter functions. Test those functions.

Upvotes: 7

D Stanley
D Stanley

Reputation: 152576

Seems like a trivial test to write, and if there are significant ramifications if isAwesome is false, then why wouldn't you write that test?

Think about this - suppose a different developer comes by 6 months from now and thinks - "I'll change it so the property is not set in the constructor - let the client decide if MyObject is awesome or not".

Now all of the code that expects every MyObject to be awesome may break. Wouldn't you want to know that such a change as made so you could decide if it was a valid change or not?

Upvotes: 1

Related Questions