Droidcon Berlin: Testing in Practice

Testing isn't always everybody's favourite task, but that doesn't need to be the case! Writing tests can be an enjoyable way to practice your coding techniques!

But with conflicting opinions on writing test code that is declarative, explicit, terse, concise, and isolated, it can be tough to know how to satisfy all of these whilst still retaining your will to live.

I'll be covering a few techniques, and mechanisms, for writing idiomatic Kotlin code that leaves you with a beautiful test case that not only fulfils all this but gives you accurate code documentation for your project.

1. Testing in Practice Keeping Your Tests Concise and Declarative Droidcon Berlin - July '24 ! Ash Davies - SumUp Android / Kotlin GDE Berlin Cat Person ashdavies.dev 1
2. Why Test? ashdavies.dev 2
3. Photos by Daniel Romero, Taylor Vick on Unsplash 3
4. "Hey, I hope you had a relaxing weekend..." — QA Enginner (8:47 Monday morning) ashdavies.dev 4
5. ashdavies.dev 5
6. Testing — Monkey — End-to-End — Acceptance — Instrumentation — Integration — Regression — Unit ashdavies.dev 6
7. ashdavies.dev 7
8. Testing Photo by DiEGO MüLLER on Unsplash 8
9. Writing Unit Tests Pros Cons They'll improve the quality of my code I don't want to It'll take like 10 mins max Literally everyone says that I should ashdavies.dev 9
10. Writing Unit Tests Conclusion I will not write unit tests ashdavies.dev 10
11. ⏱ ashdavies.dev 11
12. "Can we skip the unit tests, just for this feature?" — PM ashdavies.dev 12
13. Developer: "I'll get back to it later..." Narrator: "They never got back to it." ashdavies.dev 13
14. "Tests Saved My Ass" — Ben Kadel youtu.be/8QvXErxv9qw 14
15. "Our OKR is 100% Code Coverage" — Former CTO ashdavies.dev 15
16. ashdavies.dev 16
17. Tests test design as well as logic — Michael Feathers ashdavies.dev 17
18. Architecture Anti-Patterns and Code Smell ashdavies.dev 18
19. Architecture — Coupling — Inheritance — Mutability — Polymorphism ashdavies.dev 19
20. Problem Solving ashdavies.dev 20
21. Solutions Looking for a Problem ashdavies.dev 21
22. Problem Solving ashdavies.dev 22
23. ashdavies.dev 23
24. // Let's Code ashdavies.dev 24
25. class ThermosiphonTest { @Mock var heater: Heater @Mock var logger: Logger @InjectMocks lateinit var sut: Thermosiphon @SetUp fun setup() { MockAnnotations.init(this) } @Test fun `should heat water`() { thermosiphon.pump() assertTrue(heater.isHot()) } } ashdavies.dev 25
26. Test Doubles Mocks (╯°□°)╯︵ ┻━┻ ashdavies.dev 26
27. Test Doubles Mocks — Behaviour Verification ! — API Insensitivity " — Scale Poorly # ashdavies.dev 27
28. class ThermosiphonTest { @Mock var heater: Heater @Mock var logger: Logger @InjectMocks lateinit var sut: Thermosiphon @SetUp fun setup() { MockAnnotations.init(this) whenever(heater.heat(any())).thenReturn(/* ... */ whenever(logger.log(any())).thenAnswer { /* ... */ } @Test fun `should heat water`() { thermosiphon.pump() val argumentCaptor = argumentCaptor() verify(heater).heat(argumentCapture.capture()) assertTrue(argumentCaptor.values[0]) } } ashdavies.dev 28
29. Factory Functions ashdavies.dev 29
30. Factory Functions interface Pump { fun pump() } class Thermosiphon( private val heater: Heater, ) : Pump ashdavies.dev 30
31. Factory Functions interface Pump { fun pump() } fun Pump(heater: Heater): Pump { return Thermosiphon(heater) } private class Thermosiphon( private val heater: Heater, ) ashdavies.dev 31
32. Factory Functions CoroutineScope() CompletableDeferred() Channel() MutableStateFlow() List() ashdavies.dev 32
33. Factory Functions public actual fun <T> lazy(mode: LazyThreadSafetyMode, initializer: () -> T): Lazy<T> = when (mode) { LazyThreadSafetyMode.SYNCHRONIZED -> SynchronizedLazyImpl(initializer) LazyThreadSafetyMode.PUBLICATION -> SafePublicationLazyImpl(initializer) LazyThreadSafetyMode.NONE -> UnsafeLazyImpl(initializer) } ashdavies.dev 33
34. Functional Interfaces ashdavies.dev 34
35. Functional Interfaces fun interface Pump { fun pump() } fun Pump(heater: Heater): Pump { return Thermosiphon(heater) } private class Thermosiphon( private val heater: Heater, ) ashdavies.dev 35
36. Functional Interfaces fun interface Pump { fun pump() } fun Pump(heater: Heater) = Pump { /* ... */ } ashdavies.dev 36
37. Functional Interfaces fun interface Pump { fun pump(): Boolean } - val pump = mock<Pump> { - whenever(heat()).thenReturn(true) - } + val pump = Pump { true } ashdavies.dev 37
38. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val heater = Heater { isHot = true } val thermosiphon = Thermosiphon(heater) thermosiphon.pump() assertTrue(isHot) } } ashdavies.dev 38
39. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val heater = Heater { isHot = true } val thermosiphon = Thermosiphon(heater) thermosiphon.pump() assertTrue(isHot) } @Test fun `should cool down after heating`() { /** ... */ } } ashdavies.dev 39
40. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val heater = Heater { isHot = true } val thermosiphon = Thermosiphon(heater) thermosiphon.pump() assertTrue(isHot) } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } } ashdavies.dev 40
41. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val heater = Heater { isHot = true } val thermosiphon = Thermosiphon(heater) thermosiphon.pump() assertTrue(isHot) } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } @Test fun `should not become sentient`() { /** ... */ } } ashdavies.dev 41
42. class ThermosiphonTest { val heater = Heater { isHot = true } val thermosiphon = Thermosiphon(heater) var isSentient = false var hasExploded = false var isHot = false @Test fun `should heat water`() { /* ... */ } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } @Test fun `should not become sentient`() { /** ... */ } } ashdavies.dev 42
43. class ThermosiphonTest { val heater = Heater { isHot = true } val thermosiphon = Thermosiphon( overflow = SmallOverflowTank(), heater = heater, ) var isSentient = false var hasExploded = false var isHot = false @Test fun `should heat water`() { /* ... */ } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } @Test fun `should not become sentient`() { /** ... */ } } ashdavies.dev 43
44. class ThermosiphonTest { val heater = Heater { isHot = true } val thermosiphon = Thermosiphon( overflow = SmallOverflowTank(), aiEngine = GeminiEngine(), heater = heater, ) var isSentient = false var hasExploded = false var isHot = false @Test fun `should heat water`() { /* ... */ } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } @Test fun `should not become sentient`() { /** ... */ } } ashdavies.dev 44
45. class ThermosiphonTest { val heater = Heater { isHot = true } val thermosiphon = Thermosiphon( overflow = SmallOverflowTank(), aiEngine = GeminiEngine(), heater = heater, launchCodes = emptyList(), ) var isSentient = false var hasExploded = false var isHot = false @Test fun `should heat water`() { /* ... */ } @Test fun `should cool down after heating`() { /** ... */ } @Test fun `should not catch fire when flying`() { /** ... */ } @Test fun `should not become sentient`() { /** ... */ } } ashdavies.dev 45
46. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val thermosiphon = thermosiphon( onHeat = { isHot = true }, ) thermosiphon.pump() assertTrue(isHot) } } fun thermosiphon( onHeat: () -> Unit ) = Thermosiphon( overflow = SmallOverflowTank(), aiEngine = GeminiEngine(), heater = Heater(onHeat), launchCodes = emptyList(), ) ashdavies.dev 46
47. DRY Don't Repeat Yourself — Remove duplication — High code reusability — Isolating change ashdavies.dev 47
48. DAMP Descriptive AND Meaningful Phrases — Some duplication permitted — Declarative syntax — Meaningful naming ashdavies.dev 48
49. DRY vs DAMP ashdavies.dev 49
50. Documentation ashdavies.dev 50
51. Documentation /** * Make sure not to change this thing back to the previous implementation, * because it breaks on that one specific device in production, * when opening the user profile in France using a German locale. **/ fun doMyThing() { /* ... */ } ashdavies.dev 51
52. Documentation /** * Make sure not to change this thing back to the previous implementation, * because it breaks on that one specific device in production, * when opening the user profile in France using a German locale. * * Update: We changed this to be a remote resolution, this shouldn't happen? * We haven't seen it happen in production anymore, but just leave this * comment here, incase it occurs again... **/ fun doMyThingRefactoredV63() { /* ... */ } ashdavies.dev 52
53. Documentation /** * Make sure not to change this thing back to the previous implementation, * because it breaks on that one specific device in production, * when opening the user profile in France using a German locale. * * Update: We changed this to be a remote resolution, this shouldn't happen? * We haven't seen it happen in production anymore, but just leave this * comment here, incase it occurs again... * * Update: It's happening again, but for Italian uses in Australia, * I really hope our Italian QA enginner doesn't go on vacation to Melbourne again... **/ fun doMyThingRefactoredToBeMoreSafeIHopeV91() { if (user.locale == Locale.ITALY) { /* Hacky hack McHackFace */ } } ashdavies.dev 53
54. Documentation ashdavies.dev 54
55. Documentation: Tests fun `should store in user specific locale when device is in another country() ashdavies.dev 55
56. Documentation: Tests fun `should store in user specific locale when device is in another country() { val intendedTarget = ... val expectedLocale = ... val actualLocale = doMyThing() assertEquals(expectedLocale, actualLocal) } ashdavies.dev 56
57. commit d4c2d156e78cd579662ac7a658b00ca5aa17fd5d (HEAD -> main, origin/main, origin/HEAD) Author: Ash Davies <1892070+ashdavies@users.noreply.github.com> Date: Sun Jun 23 19:19:44 2024 +0200 ashdavies.dev 57
58. ashdavies.dev 58
59. class ThermosiphonTest { @Test fun `should heat water`() { var isHot = false val thermosiphon = thermosiphon( onHeat = { isHot = true }, ) thermosiphon.pump() assertTrue(isHot) } } fun thermosiphon( onHeat: () -> Unit ) = Thermosiphon( overflow = SmallOverflowTank(), aiEngine = GeminiEngine(), heater = Heater(onHeat), launchCodes = emptyList(), ) ashdavies.dev 59
60. What about Context?! ashdavies.dev 60
61. Test Doubles Mocks fun Context(checkSelfPermission: (String) -> Int): Context = mock { whenever(it.checkSelfPermission(any())).thenAnswer { invocation -> checkSelfPermission(invocation.arguments[0] as String) } } val context = Context { PackageManager.PERMISSION_GRANTED } ashdavies.dev 61
62. Refactoring Interface Segregation ashdavies.dev 62
63. Refactoring Interface Segregation class MenuProvider( private val navStateStore: NavStateStore = NavStateStore(), ) { fun get() = combine(navStateStore.isEnabled, /* ... */) { /* ... */ } } class NavStateStore { val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 63
64. Refactoring Interface Segregation class MenuProvider( private val navStateStore: NavStateStore = NavStateStore(), ) { fun get() = combine(navStateStore.isEnabled, /* ... */) { /* ... */ } } class NavStateStore { val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 64
65. Refactoring Interface Segregation interface NavStateStore { val isEnabled: Flow<Boolean> } class InMemoryNavStateStore : NavStateStore { override val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 65
66. Refactoring Interface Segregation interface NavStateStore { val isEnabled: Flow<Boolean> } class PreferencesNavStateStore : NavStateStore { override val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 66
67. Refactoring Interface Segregation ✨ interface NavStateStore { val isEnabled: Flow<Boolean> } class SentientNavStateStore : NavStateStore { override val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 67
68. Refactoring Interface Segregation interface NavStateStore { val isEnabled: Flow<Boolean> } class NavStateStoreImpl : NavStateStore { override val isEnabled: Flow<Boolean> = /* ... */ fun setIsEnabled(value: Boolean) { /* ... */ } fun getLastSet(): Long { /* ... */ } } ashdavies.dev 68
69. Refactoring Objects class MenuProvider( private val menuDefaults: MenuStateDefaults = MenuStateDefaults, ) { /* ... */ } object MenuStateDefaults { val iconWidth = 24 } ashdavies.dev 69
70. Refactoring Objects class MenuProvider( private val menuProperties: MenuStateProperties = MenuStateProperties.Default, ) { /* ... */ } interface MenuStateProperties { val iconWidth: Int companion object Default : MenuStateProperties { override val iconWidth = 24 } } ashdavies.dev 70
71. Refactoring Objects ! class MenuProvider( private val menuProperties: MenuStateProperties = MenuStateProperties(), ) { /* ... */ } interface MenuStateProperties { val iconWidth: Int companion object { operator fun invoke(): MenuStateProperties { /* ... */ } } } ashdavies.dev 71
72. Refactoring Factory Function private object MenuStateDefaults { val iconWidth = 24 } class MenuProvider( private val menuProperties: MenuStateProperties = MenuStateProperties(), ) { /* ... */ } fun interface MenuStateProperties { val iconWidth: Int } fun MenuStateProperties( iconWidth: Int = MenuStateDefaults.iconWidth, ) = object : MenuStateProperties { override val iconWidth = iconWidth } ashdavies.dev 72
73. Testing Assertions data class WaterState( val temperature: Int, ) fun interface Heater { fun heat(water: WaterState): WaterState } @Test fun `should produce water for English Breakfast Tea`() { val heater = Heater { it.copy(temperature = 95) } val thermosiphon = Thermosiphon(heater) val initial = WaterState(21) val state = thermosiphon.pump(initial) assertTrue(state.temperature >= 95) } ashdavies.dev 73
74. Testing Assertions data class WaterState( val temperature: Int, + val filtered: Boolean, ) fun interface Heater { fun heat(water: WaterState): WaterState } @Test fun `should produce water for English Breakfast Tea`() { val heater = Heater { it.copy(temperature = 95) } val thermosiphon = Thermosiphon(heater) val initial = WaterState(21, false) val state = thermosiphon.pump(initial) assertTrue(state.temperature >= 95) } ashdavies.dev 74
75. Testing Assertions data class WaterState( val filtered: Boolean, val temperature: Int, ) fun interface Heater { fun heat(water: WaterState): WaterState } @Test fun `should produce water for English Breakfast Tea`() { val heater = Heater { it.copy(temperature = 95) } val thermosiphon = Thermosiphon(heater) val initial = WaterState(21, true) val expected = WaterState( filtered = true, temperature = 95, ) assertEquals(expected, thermosiphon.pump(initial)) } ashdavies.dev 75
76. Testing Assertions data class WaterState( val filtered: Boolean, val temperature: Int, ) fun interface Heater { fun heat(water: WaterState): WaterState } @Test fun `should produce water for English Breakfast Tea`() { val heater = Heater { it.copy(temperature = 95) } val thermosiphon = Thermosiphon(heater) val initial = WaterState(21, true) val expected = WaterState( filtered = true, temperature = 95, ) assertEquals(expected, thermosiphon.pump(initial)) } ashdavies.dev 76
77. Conclusion General — Prefer functional interfaces wherever possible — Utilise factory functions to isolate behaviour — Segregate behaviour into smaller interfaces ashdavies.dev 77
78. Conclusion Testing — Avoid using mocks unless absolutely necessary — Restrict test behaviour to function body — Keep individual tests idempotent — It's OK to repeat yourself ashdavies.dev 78
79. But wait, there's more! Out-Takes ashdavies.dev 79
80. Out-Takes: Flaky the Little Flake android- review.googlesource.com/c/ platform/frameworks/support/ +/2776638 ashdavies.dev 80
81. Out-Takes: TDD private fun isEven(number: Int): Boolean { // Added to pass unit test if (number == 11) { return false } // Added to pass unit test if (number == 11) { return false } // Fix for Ticket 12846 if (number == 11407) { return false } // Fix for Ticket 14336 if (number == 9) { return false } return true } ashdavies.dev 81
82. Out-Takes: Unreachable State ashdavies.dev 82
83. Thank You! Ash Davies - SumUp Android / Kotlin GDE Berlin ashdavies.dev 83
84. Additional — blog.kotlin-academy.com/item-30-consider-factory- functions-instead-of-constructors-e1c747fc475 — medium.com/@june.pravin/mocking-is-not-practical- use-fakes-e30cc6eaaf4e — testing.googleblog.com/2024/02/increase-test- fidelity-by-avoiding-mocks.html — handstandsam.com/2020/06/08/wrapping-mockito- mocks-for-reusability/ ashdavies.dev 84