What is TDD ? What are the benefits and cost of TDD ? How to do TDD correctly in Swift ?

1. TDD
TEST DRIVEN DEVELOPMENT
Jianbin LIN

2. DRAFT INTERFACE
WRITE TEST THAT
FAILS
IMPLEMENT AND
PASS THE TEST
REFACTOR

3. func calculateAreaOfSquare(w: Int, h: Int) -> Double { }
START FROM THE INTERFACE
Given w=2, h=2, Expect area to be 4.
WRITE FIRST TEST

4. IT FAILS.
COMPILATION ERROR IS TDD ERROR
func calculateAreaOfSquare(w: Int, h: Int) -> Double { }

5. START IMPLEMENTING
func calculateAreaOfSquare(w: Int, h: Int) -> Double {
return w * h
}

6. IT PASSED.
REFACTOR
func calculateAreaOfRectangle(w: Int, h: Int) -> Double { }
func calculateAreaOfSquare(w: Int, h: Int) -> Double { }

7. Given w=-1,h=-1, Expect area to be 0.
WRITE ANOTHER
TEST

8. FAILS
func calculateAreaOfRectangle(w: Int, h: Int) -> Double {
return w * h
}
It returns 1

9. NEW IMPLEMENTATION
func calculateAreaOfRectangle(w: Int, h: Int) -> Double {
if w > 0 && h > 0 {
return w * h
}
return 0
}

10. IT PASSED.
REFACTOR
CONTINUE THIS CYCLE UNTIL ALL THE
CRITERIA ARE MET

11. WHY TDD?

12. DON’T MISS UNIT-TEST ?
DON’T MISS ANY REQUIREMENT!

13. FEWER BUGS

14. High productivity

15. INTERFACE
FIRST

16. REFACTORING FRIENDLY

17. WHAT DOES TDD COST ?
WHEN TDD IS DONE CORRECTLY !

18. OTHERWISE…
10X OF WORK THAN BEFORE

19. DO DDT CORRECTLY

20. TDD
ONLY INTERFACE NEED TO BE TESTED
▸ All the methods not used as interface should be private

21. TDD
USE GOOD ARCHITECTURE
▸ Less chance for big refactoring
▸ Less chance to destroy the tests
VIP or VIPER

22. TDD
DO REAL UNIT TEST
▸ What is a unit ?

23. TDD
Use interface(protocol) to isolate class to test

24. TDD
Use interface(protocol) to isolate class to test

25. TDD
let interactor = Interactor()
interactor.presenter = MockPresenter()
Verify function is called with parameter message
interactor.presenter.presentError(message)
verify(interactor.presenter.presentError(message))

26. TDD
CREATE MOCK MANUALLY OR WITH TOOL
▸ Tool: Cuckoo
▸ https://github.com/Brightify/Cuckoo
▸ Auto-generate mock objects for Swift Protocol
▸ Simulate stub behaviors on each method
▸ Verify if a method is called with certain parameters

27. TDD
WRITE STRUCTURED TEST

28. TDD
EFFECTIVE TESTS USING XCTEST
▸ Test_MethodName_StateUnderTest_ExpectedBehavior
Naming convention

29. TDD
EFFECTIVE TESTS USING XCTEST
Arrange, Act, and Assert
class BananaTests: XCTestCase {
func testPeel() {
// Arrange: Create the banana we'll be peeling.
let banana = Banana()
// Act: Peel the banana.
banana.peel()
// Assert: Verify that the banana is now edible.
XCTAssertTrue(banana.isEdible)
}
}

30. TDD
STRUCTURE TEST WITH TOOLS
▸ Tool: Quick & Nimble
▸ https://github.com/Quick/Quick
▸ Force developer adding clear comments for each key
section

31. TDD
STRUCTURE TEST WITH TOOLS
▸ Tool: Quick & Nimble
func testDolphin_click_whenTheDolphinIsNearSomethingInteresting_isEmittedThreeTimes() {
// ...
}
describe("a dolphin") {
describe("its click") {
context("when the dolphin is near something interesting") {
it("is emitted three times") {
// ...
}
}
}
}

32. TDD
KEY ELEMENTS IN QUICK
▸ describe closure: Describing Classes and Methods
▸ context closure: Specifying Conditional Behavior
▸ it closure: Assert if requirement is met
describe("a dolphin") {
describe("its click") {
context("when the dolphin is near something interesting") {
it("is emitted three times") {
// verify or assert
}
}
}
}

33. TDD
REAL-WORLD EXAMPLE ON UNIVADIS
▸ branch: feature/cuckoo

34. TDD
ARE YOU READY FOR TDD ?