Refactoring test inputs with Test Data Builders

Test data builders is a pattern you can use to easily arrange test data, while improving their readability and reducing coupling between tests and source code.

Learning Goals

• Name the 4 rules of the test data builder pattern
• Use test data builders to create test inputs

Session outline

• 3 to 7 min connect activity
• 13 min concept: 4 rules of a Test Data Builder + demo
• 35 to 39 min concrete practice: refactor test data creation with test data builders
• 5 min reflect: does our code have this issue?

Connect

Pick one of the following connect activities, depending on the trainee’s knowledge:

• 3 facts and a question about arranging inputs test
• 3 facts about the builder pattern
• map code examples with pattern names

Map code examples with pattern names

Preparation

• Write notes with the name of some following patterns which can be used to create test inputs:
  • a class constructor
  • a class constructor with default values
  • a factory method
  • object mother
• For each pattern, provide a note with an example
• Randomize names and patterns

Activity

• Ask attendees to map code examples of test inputs construction with the corresponding patterns. (3 min)
• Discuss pros and cons of each pattern usage in a unit test suite context, (you could use examples from the team’s production code). (4 min)

Concepts

Presentation: 4 rules of a Test Data Builder (3 min)

Explain the 4 rules of test data builders:

1. Has an instance variable for each constructor parameter
2. Initialises its instance variables to commonly used or safe values
3. Has a build method that creates a new object using the values in its instance variables
4. Has chainable public methods for overriding the values in its instance variables (aka with…() methods).

Demo (10 min)

Demo the refactoring of test inputs using a test data builder on an existing test.

• use only with…() method names in a first time
• remove usage of overriding method when the value set is not relevant for the test case (you can change the argument value with no side effect on the test execution)

Tips

• You can use the BookInvoicing-TestDesign-Kata, (also known as test-data-builders-kata), choosing the language of your choice, refactoring the Country object construction in tests.
• You may use the generate code from usage method to focus on writing the code as you need to use it, and keep the demo short and clear.

Concrete Practice

Ask attendees to:

• reproduce the demo on the same test data, working in pair or mob programming
• apply the same technique to all objects created in the Arrange part of the tests

Conclusion

Does our code have this issue?

Ask the team to find part of their tests where they could have applied the test data builder pattern