Testable-Code

Examples of how to write testable code

Why Unit Testing?

• Testable code forces you to write clean separated code => maintainability
• Tests can be automated to run after every change => safety net
• Bottom-up approach: first test parts of the program before testing the program itself

Demo 01: Test Driven Development

Write small automated tests first

This requires the developer to fully understand requirements. Initially a new test fails, so add code & refactor until the test pass. Tests serve as documentation.

Demo Example Requirements

Write a 'StringCalculator' class that accepts integers and return their sum:

• The Add method accepts a comma-delimited string of integers.
• For an empty string the Add method will return 0.
• The Add method will return their sum of numbers.
• The Add method supports user specified delimiters.
• The Add method must be able to skip a pre-defined number of fields from the start of the string.

Demo 02: Layered Architecture

Traditional Layered Architecture

Creates unnecessary coupling

• The Presentation layer depends on ...
• The Business layer depends on ...
• The Data layer ... And everything depends on common utility and infrastructure classes.

To solve coupling, one could introduce Dependency Injection of these classes.

The Onion Architecture

http://jeffreypalermo.com/blog/the-onion-architecture-part-1/

Dependency Injection is integral part of this architecture. It encourages a better separation of concerns:

• Infrastructure concerns are implemented in classes that can be injected into the lower layers
• The Presentation layer depends on ...
• The Application Services layer depends on ...
• The Domain Services layer depends on ...
• The Domain Model ... And common utility and infrastructure classes are injected into the application services.

Demo Example Requirements

Users upload a character separated values (CSV) file containing expenses reports of our employees

• The applications accepts a CSV file.

  • The first column is the user id
  • The second column is the expenses category
  • The 12 next columns are the monthly expenses expressed in euro

  EmployeeId	Category	January	February	March	April	May	June	July	August	September	October	November	December
  1	Travel	92	92	92	92	92	92	92	92	92	92	92	92
  1	Parking	20	20	20	20	35	00	20	35	20	20	20	20
  2	Travel	1500	0	0	1700	0	0	1400	0	0	2400	0	0
  2	Parking	200	0	0	150	0	0	235	0	0	175	0	0
  2	Hotel	700	0	0	750	0	0	335	0	0	1075	0	0

Demo 03: Presentation

Non Testable UI

Using the view as a datacontainer and putting code directly in the code-behind will create a tight coupling between the presentation logic and the actual view. This makes it impossible to write automated tests for the presentation logic.

Model-View-ViewModel

Decouple the View from the presentation logic by applying the Model-View-ViewModel pattern. This demo is inspired by "Jason Dolinger on Model-View-ViewModel"

• Move data out of the code-behind of the view and into the ViewModel and expose them as public properties
• Bind the controls on the view to the public properties of the ViewModel
• Inject external dependencies into the ViewModel
• Inject the ViewModel into the View from App.xaml.cs