Hidden Secrets of Unit Testing

Transcript

1. Hidden Secrets of Unit Testing The Long Journey to Writing

   Tests That Matter

2. What are Unit Tests Unit = Smallest Testable Part of

   Application In most cases -> methods sometimes -> state of object

3. Input / Output result = Calculator.sumOf 1, 1 expect(result).toBe 2

   -------------------------------------------------------- Only tests the output of a method when called with specific parameters.

4. Peer Communication mock = Controller.create() view = View.create delegate: mock

   view.onDonateButtonClicked() expect(mock.donate).toHaveBeenCalled() -------------------------------------------------------- Tests the protocol / communication between test subject (view) and its dependencies (delegate)

5. Changed State car = Car.create() expect(car.position).toEqual x: 0, y: 0

   -------------------------------------------------------- car = Car.create() car.moveTo x: 3, y: 4 expect(car.position).toEqual x: 3, y: 4 -------------------------------------------------------- Use only for testing public attributes (models)

6. Three Golden Rules Explicit Dependencies Tell, Don't Ask Listen to

   Your Tests

7. Explicit Dependencies class TestView constructor: -> # wrong -> hidden

   / hard dependency @delegate = App.Controller.create() -------------------------------------------------------- class TestView # explicit dependency from outside constructor: (@delegate) -> throw "need delegate" unless @delegate?

8. Tell, Don't Ask carWindow = CarWindow.create() car = Car.create window:

   carWindow car.window.close() // asking = wrong car.closeWindow() // telling = right! -------------------------------------------------------- Law of Demeter: Principle of Least Knowledge Know only the surface, not the internals

9. Listen to Your Tests Discover Code / Architecture Smells: •

   Complex test -> method does too much? • Many mocks in test -> too many dependencies? • Dependency can't be mocked -> hard coupling! • Testing state of objects -> Split into classes that work together, test this communication instead • Test are not readable -> The method names should express the specific domain clearly!

10. Thank you! Dominik Guzei @DominikGuzei (Twitter)