Design Tech Talk Series Presents: OO Design for Testability

Google Tech Talk
October 6, 2009

ABSTRACT

Presented by Miško Hevery.

We design our code for performance, maintenance, simplicity, extensibility and other goals, but most of us do not think about testability as a design goal, yet verifying the correctness of our code is of great importance. What does it mean to have testable code, and what kind of trade offs does one have to think about when designing for testability. Turns out that testable code is well designed code, and it has many of the characteristics we search for such as low cohesion, separation of concerns, proper encapsulation and many others.

• Category

  Science & Technology

[neohubris]

Misko thank you very much for doing these talks. Your clean code talks has helped my work tremendously.

[Pablo Pera]

Great talk!

[Roberto Guerra]

That is not the Law of Demeter. It is about types not dots.

[Sumit Vyas]

Awesome... For the 20 arguments problem the solution suggested is following SRP. Single Responsibility Principle takes care of simplifying the Object graph and code simplification.

[ericcartmansh]

at 23:04 wouldn't it make more sense to have the unit test create the Engine instance fakeEngine with getEngine() and pass in the engine factory and the model? Or is the call to getEngine assumed to be happening in the constructor of the Engine class?

[Christian B]

I've seen some videos from Miško Hevery. This helped me alot moving to the right direction.

[vaulttech]

I've searched for the other 3 talks (since this is the fourh) but I couldn't find them. Can someone please give me the link?

[Grim Leaper]

I meant LoginPage, sorry.

[Grim Leaper]

Well I think he refered to the latter case as "the class with singleton lifetime" and not a singleton (I noticed this ambiguity only when he talked about the Login_class). And he did not say it was problematic to test because it had singleton lifetime, he said it was problematic owing to it's dependencies, and therefore that particular class might have been better as short-lived class with different dependencies, that wouldn't force it to break the law of Demeter.Am I getting it right?

[Erick Dovale]

Very nice talk. A bit ambiguous with the term singleton. There is the singleton pattern as described in the Gof4 book which is the one that is problematic to test and there is the single instance of a class throughout the life of the application. There is nothing wrong with the latter IMO.

[Sai Gudigundla]

Thanks for the great presentation. 

[pereznels]

Awesome presentation!