Introducción práctica a Test-Driven Development

Software Craftsmanship Alicante

Who am I?

• Rubén Antón A.K.A @rubocoptero

• Crafting code for Flywire

• h4ckademy alumni

What’s TDD?

TDD is not testing!

Two simple rules

• Don’t write a line of new code unless you first have a failing automated test.

• Eliminate duplication.

What is TDD?

• XP practice that combines Test-First and Refactoring

• Tests as a design tool

• KISS

• Baby steps

Mantra

Steps

1. ROJO: write a little test that doesn’t work, perhaps doesn’t even compile at first

2. GREEN: make the test work quickly, committing whatever sins necessary in the process

3. REFACTOR: eliminate all the duplication created in just getting the test to work.

Why use TDD?

Benefits• Manually verification is time consuming

• Break down our work into manageable chunks

• Source of documentation

• Avoid over-engineering

• Safety net

• Encourages Loosely Coupled Design

–Chris Jordan

“Software is inherently complex, and being able to make things easier for ourselves as

developers is a crucial part of our role to deliver high quality software.”

Techniques

Fake it (’til you make it)1. Return a constant to make it pass

2. Gradually replace constants with variables until you have the real code

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1));}

private int Sum(int x, int y){ return 4}

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1));}

private int Sum(int x, int y){ return 3 + 1;

}

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1)); Assert.Equals(5, Sum(3, 2));}

private int Sum(int x, int y){ return x + y;}

Triangulation• Use two or three test cases before to generalize.

• Only use it when completely unsure of how to refactor.

• What axes of variability are you trying to support in your design?

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1));}

private int Sum(int x, int y){ return 4}

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1)); Assert.Equals(5, Sum(3, 2));}

private int Sum(int x, int y){ return x + y;}

[TestMethod]public void TestSum(){ Assert.Equals(4, Sum(3, 1)); Assert.Equals(5, Sum(3, 2));}

private int Sum(int x, int y){ return x + y;}

Obvious Implementation

• Fake it and Triangulation use baby steps.

• If you think it’s obvious, type in the real implementation.

• It’s a "second gear".

• If you get an unexpected red bar, back up.

–Kent Beck

“Remember, TDD is not about taking teensy tiny steps, it’s about being able to take teensy tiny steps. Would I code day-to-day with steps this

small? No. But when things get the least bit weird, I’m glad I can.”

Let’s practice…just a few last things before to start.

Rules

• 30 seconds to go from RED to GREEN

• Don’t lose the GREEN in the refactoring phase.

• No debug

Good tests• Imagine the perfect interface for our operation

• Fast

• Independents

• Arrange - Act - Assert

// ArrangeMyProductionClass myProductionClass = new MyProductionClass();

// Actbool result = myProductionClass.GetBooleanResult();

// AssertAssert.IsTrue(result);

Before you start• The focus is to practice writing the best code we

can possibly write and challenge ourselves. It is important to mention that the goal is not to finish the exercise as soon as posible, but to learn during the process via the discussion with our partner.

• Do one task at a time. The trick is to learn to work incrementally.

• Make sure you only test for correct inputs. there is no need to test for invalid inputs for this kata

FizzBuzzReturn “fizz”, “buzz” or “fizzbuzz”.

For a given natural number greater zero return:

• “fizz” if it is dividable by 3

• “buzz” if it is dividable by 5

• “fizzbuzz” if it is dividable by 3 and 5.

Input Result

1 1

2 2

3 fizz

6 fizz

5 buzz

10 buzz

15 fizzbuzz

30 fizzbuzz

FizzBuzz continuation

• A number is "fizz" if it is divisible by 3 or if it has a 3 in it.

• A number is "buzz" if it is divisible by 5 or if it has a 5 in it.

Retrospective time

• What difficulties do we found?

• What we have done?

• What we have learnt?

TDD economy• Either you will have to be able to write twice as

many lines per day as before, or write half as many lines for the same functionality.

• You’ll have to measure and see what effect TDD has on your own practice.

• Be sure to factor debugging, integrating, and explaining time into your metrics, though.

More than TDD

• Extreme Programming practices

• SOLID

• Clean Code

• 4 rules of simple design

How can I learn it?• Practice, practice and practice!

• Read good books

• TDD by example - Kent Beck

• Clean Code - Uncle Bob

• Refactoring - Martin Fowler

• Test Driven - Lasse Koskela

• …

Thank you all!