Tag Archives: Screen Cast

TDD as if you Meant It: Refactoring to Builder (Episode 5)

TDD as if you Meant It: Refactoring to Builder (Episode 5)

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Cost of Change during evolution

There are some language structures that make Evolutionary Design difficult. One of them is the constructor. When I evolve the code, I often understand that one more parameter is needed for the constructor. Because of this I need to minimize the cost of change of the constructor. The best way I know to do that is by creating a builder. In this way I will call the constructor only once, in the builder. So my cost of change is really small.

Duplication

If I need to introduce a new design concept, I make sure before that I minimized the duplication connected to that new design concept. Calling new Board(…) many times is a clear sign of duplication. This duplication would make the code evolution considerably slower.

State Immutability

Testing becomes easier when state does not change during the life cycle of the object. Or, there are no setters on any object. That is why I use constructors and private fields.

Fluent Builder

A builder is called fluent when it looks like playerBuilder.withName(“Adi”).withAge(7).withColor(“Red”).build(). If let’s say I need to introduce a new characteristic to my player, I can always add a new method to the PlayerBuilder. And I would have something like playerBuilder.withName(“Adi”).withAge(7).withColor(“Red”).withExperienceLevel(“Beginner”).build().

Focused Tests with Idempotence

Having this type of builder also lets me have focused tests. I don’t want my test that needs only Age to contain Name. So I want to be able to have playerBuilder.withAge(34).build(). In this case all the values for all the other fields of Player will have a default value that is not generating any side-effects in the system. We could call this characteristic an idempotence of the builder.

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TDD as if you Meant It: Refactor to a new Class (Episode 4)

TDD as if you Meant It: Refactor to a new Class (Episode 4)

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Extract Class

Starting from the methods that I extracted in the testing class I make them static and then extract them to a new class. The methods from the extracted class are then static. I change the static call with a call to an instance created in the setup of the test. There is a small trick I use when doing that, so that I am always on green while refactoring. Check the codecast to spot it!

The Rule of Three – extract class

In this case as well The Rule of Three applies: only extract duplication when spotted at least three times. When extracting methods to a new class I need at least three methods that belong together.

As mentioned in the previous articles, this is just a guideline. If you are sure, extremely sure, that one method should be extracted, then go for it. But be careful not to generalize to soon. Premature generalization is the root of all evil (Donald Knuth paraphrase).

Testability – Guidelines

Because all the tests are calling the extracted class, it is tested as well, but indirectly. This is a classicist TDD approach where I don’t mind if I test a few classes together, without any dependency injection, stubbing or mocking. Another approach would be to start adding tests to the extracted class, after it was extracted. It is a question of style, but there are also some guidelines to this.
The extracted class needs to either have only logic, or only to hold data.
Whenever I don’t have any logic in the extracted class, I won’t add new tests.
If the extracted class has logic, but it is trivial, I will use the existing indirect tests.
If the extracted class has a lot of logic, I will split the existing tests to have specific tests for the extracted class, and smaller (simpler) initial tests.

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TDD as if you Meant It: Refactor Primitives to Concepts (Episode 3)

TDD as if you Meant It: Refactor Primitives to Concepts (Episode 3)

About

Hidden Concepts

Each primitive is always hiding a business concept (or call them Domain Entities if you wish). During this episode these primitives will get better names (“Maximize Clarity” from the Four Elements of Simple Design) and when I see duplication between them, it will be removed (“Minimize Duplication” from the Four Elements of Simple Design).

Whenever these concepts remain hidden, the cost of change is big. The more hidden design concepts we have, the bigger the cost of change. I optimize my code for fast and cheap changeability. Because this example is written using Object Oriented Programming concepts, each of these concepts needs at the end to become a class.

Classical Evolutionary Design Layers

The business concepts grow in layers from: primitives, to variables, methods and then classes. With TDD as if you Meant It we always use the rule of three when evolving from one layer to another. I always use refactorings to make duplication explicit and then minimize it. I never skip a layer, because that would be a much too bigger step. We could call this approach Evolutionary Design in Baby Steps.

This approach is useful when starting bottom-up, when there are no, or not may classes and methods, but tests. This approach would not be suitable usually when having a top-down approach.

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TDD as if you Meant It: I care about Behavior and not about Representation (Episode 2)

TDD as if you Meant It: I care about Behavior and not about Representation (Episode 2)

About

Intentional Primitive Obsession

In the first episode I added some tests where I represent state as strings. This is an intentional approach to hide the complexity of the concepts with primitives. Since with TDD as if you Meant It I am not allowed to add any new classes, I need to start the problem by using primitives. I could have used an array to define the Board concept, but that already means that I am taking more complex design decisions.

Triangulating

I am focusing on triangulating on the concept of GameResult in order to have enough proof in order to extract it to a method. The typical proof I am searching for is duplication. I apply the Rule of Three to spot duplication and then to generalize my code.

Deductive vs Inductive

Deductive: when doing evolutionary design I am deductive. I start from a small idea and add on it. Whenever I can deduce some higher order concepts, I extract them. These higher order concepts are usually a crystallization of the raw primitives.

Inductive: when doing design up-front I am inductive. I start from some bigger idea and then I try to prove it with code. Read More →

TDD as if you Meant It: Think – Red – Green – Refactor (Episode 1)

TDD as if you Meant It: Think – Red – Green – Refactor (Episode 1)

About

TDD as if you meant it is a very strict way of writing code in a Test Driven Development approach. One needs to follow the rules below:

Guidelines

In the first episode the main focus in to respect a few guidelines:

  1. Guideline 1: Always start with outputs when doing an analysis
  2. Guideline 2: Behavior Slicing
  3. Guideline 3: SIMPLIFY!
  4. Guideline 4: Introduce only one notion (domain concept) at a time, one per test
  5. Guideline 5: The rule of three “only extract duplication when spotted at least three times”
  6. Guideline 6: Triangulation

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