Interfaces in TDD

[Angus Ferguson]

Hi @ll,

having this Class:

public class BioPic implements Comparable<BioPic> {

    public int likeCounter;
    public Integer counter;

    public int getShare() {
        return share;
    }

    public void setShare(int share) {
        this.share = share;
    }

    public int getComment() {
        return comment;
    }

    public void setComment(int comment) {
        this.comment = comment;
    }

    public String getTheme() {
        return theme;
    }

    public void setTheme(String theme) {
        this.theme = theme;
    }

    public int share;
    public int comment;
    public String tittle;
    public String theme;

    public BioPic(int likeCounter,int share,int comment,String tittle,String theme) {

        likeCounter = 9;
        share = 0;
        comment = 0;
        tittle = "";
        theme = "";

    }

    @Override
    public int compareTo(BioPic o) {
        if (likeCounter < o.likeCounter) {
            return -1;
        }
        if (likeCounter > o.likeCounter) {
            return 1;
        }
        return 0;
    }

I want to use TDD. I am finding out how to create TDD tests for classes with interfaces. I have searched on the web for a while but I find it confusing.

Could someone, give a resource where I could get clear examples or info, please?

Regards, ISaac

[Junilu Lacar]

What exactly do you mean when you say "I want to create TDD tests"?

TDD is an approach, a way of thinking about design and code. It's not an adjective as you have used it.

[Tim Cooke]

You've jumped the gun already with TDD because you've written some implementation without writing a test first. TDD stands for Test Driven Development which discusses a method of programming where your tests drive your implementation which implies you write your tests first.

You'll have probably found already a whole bunch of information about TDD on the internet, some proposing it, some condemning it, and lots of conflicting information in-between. My recommendation to grasp the original essence of TDD without getting clouded by all the chaff that followed is to pick yourself up a copy of Kent Beck's "Test-Driven Development by Example". The book is from way back in 2003 but don't be put off, it's a great read.

[Angus Ferguson]

Yes, I meant that I am following TDD for the desing of a small app, and I would like to have feed back, because I need to add Interfaces in order to implement the Comparator interface....

[Angus Ferguson]

Ok I get the book!

[Junilu Lacar]

No knock on Kent Beck's book but IMO the best book that will help you understand and get better at TDD is a one that's not explicitly about TDD: Corey Haines "Understanding the 4 Rules of Simple Design"

If you're a beginner, I doubt you'll find anything specifically about testing interfaces in either book though. I think that's a nuance that you'll only recognize when you understand how TDD is supposed to be done. Here's my take on testing interfaces:

1. Tests that are written against an interface will be "abstract" by nature because interfaces are not executable, unless your interface has default methods as introduced in Java 8.  Generally, however, the tests you define for an interface should pass when run against any and all current and future implementations.

2. Following from #1, you'd probably want to set up a unit test for an interface's API as an abstract class that will be extended by tests that provide a specific implementation.

I don't see the code that you provided as being specifically tied to a test around an interface.  I would probably write tests like this:

@Test
public void can_compareTo_other_BioPic() { ... }

@Test
public void compareTo_returns_negative_1_when_has_fewer_likes() { ... }

@Test
public void compareTo_returns_1_when_has_more_likes() { ... }

@Test
public void compareTo_returns_0_when_has_same_number_of_likes() { ... }

As I said, TDD is a way to think about design and drive that thinking with tests.  These tests would probably make me think about the need to implement equals() and hashcode() since it would be surprising to have a compareTo() that is based on # of likes but still have equals() be inherited from Object, which only checks for reference equality -- there's a lack of symmetry there that should be address to make the BioPic class more complete and avoid surprises later on.