Fakes and Mocks and Spies - Oh My! -- Chicago

Let’s talk about testing support. There’s no shortage of opinions on how to handle subject dependencies, but no option fits all scenarios. Do we use a mocking framework, or write out test-specific implementations? I’ll share tips on writing maintainable, useful tests quickly.

Transcript

1. rbusarow Rick Busarow FAKES MOCKS SPIES OH MY! GOTO Chicago Dec 10, 2019
2. @rbusarow Tests should…
3. Tests should… break when the app breaks pass when the app is working be easy to read be fast to write @rbusarow
4. Tests should be easy to read Tests should be fast to write @rbusarow
5. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 2 assertEquals(4, result) } }
6. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 2 assertEquals(4, result) } } JUnit assertEquals
7. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(4, result) } }
8. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(4, result) } } java.lang.AssertionError: Expected :4 Actual :5
9. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(4, result) } }
10. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(result, 4) } }
11. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(result, 4) } } wrong order!
12. @rbusarow import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 assertEquals(result, 4) } } java.lang.AssertionError: Expected :5 Actual :4 wrong order!
13. @rbusarow infix assertions import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 result shouldBe 4 } }
14. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 result shouldBe 4 } }
15. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test class ExampleUnitTest { @Test fun addition_isCorrect() { val result = 2 + 3 result shouldBe 4 } } org.opentest4j.AssertionFailedError: expected: 4 but was: 5 Expected :5 Actual :4
16. @rbusarow There’s more…
17. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test @Test fun more() { someBoolean shouldBe true }
18. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test @Test fun more() { someBoolean shouldBe true someNullable shouldBe null }
19. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test @Test fun more() { someBoolean shouldBe true someNullable shouldBe null someList shouldBe listOf(1, 2, 3) }
20. @rbusarow infix assertions import io.kotlintest.shouldBe import org.junit.Test @Test fun more() { someBoolean shouldBe true someNullable shouldBe null someList shouldBe listOf(1, 2, 3) someArray shouldBe arrayOf(1, 2, 3) }
21. @rbusarow Auto-complete still works
22. @rbusarow infix assertions
23. @rbusarow KotlinTest github.com/kotlintest/kotlintest Kluent markusamshove.github.io/Kluent/
24. @rbusarow Mocking
25. @rbusarow Mocking class AnalyticsSolution private constructor() { fun report(message: String): Unit = ... companion object { fun initialize(context: Context): Unit = ... fun instance(): AnalyticsSolution = ... } }
26. @rbusarow Mocking class AnalyticsSolution private constructor() { fun report(message: String): Unit = ... companion object { fun initialize(context: Context): Unit = ... fun instance(): AnalyticsSolution = ... } } Final by default
27. @rbusarow Mocking class AnalyticsSolution private constructor() { fun report(message: String): Unit = ... companion object { fun initialize(context: Context): Unit = ... fun instance(): AnalyticsSolution = ... } } Private constructor Final by default
28. @rbusarow Mocking class AnalyticsSolution private constructor() { fun report(message: String): Unit = ... companion object { fun initialize(context: Context): Unit = ... fun instance(): AnalyticsSolution = ... } } Private constructor Final by default Not JVM
29. @rbusarow Mocking class AnalyticsSolution private constructor() { fun report(message: String): Unit = ... companion object { fun initialize(context: Context): Unit = ... fun instance(): AnalyticsSolution = ... } } interface AnalyticsWrapper { fun report(event: String) } class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution ) : AnalyticsWrapper { override fun report(event: String) { analytics.report(event)
30. @rbusarow Mocking } } interface AnalyticsWrapper { fun report(event: String) } class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution ) : AnalyticsWrapper { override fun report(event: String) { analytics.report(event) } }
31. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `wrapper report should delegate to AnalyticsSolution`() { } }
32. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `wrapper report should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) } }
33. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `wrapper report should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val subject = AnalyticsWrapperImpl(solution) } }
34. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `wrapper report should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val subject = AnalyticsWrapperImpl(solution) subject.report("test event") } }
35. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `wrapper report should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val subject = AnalyticsWrapperImpl(solution) subject.report("test event") verify { solution.report("test event") } } }
36. @rbusarow MockK mockk.io
37. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution ) : AnalyticsWrapper { override fun report(event: String) { analytics.report(event) } }
38. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution, private val appVersion: AppVersion ) : AnalyticsWrapper { override fun report(event: String) { if (appVersion.debug) { Log.v("AnalyticsWrapper", event) } else { analytics.report(event) } } }
39. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution, private val appVersion: AppVersion ) : AnalyticsWrapper { override fun report(event: String) { if (appVersion.debug) { Log.v("AnalyticsWrapper", event) } else { analytics.report(event) } } } ????
40. @rbusarow given: a = b b = c then: a = c transitive relation transitive property
41. @rbusarow given: if a then b if b then c then: if a then c chain rule transitive implication hypothetical syllogism double modus ponens
42. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution, private val appVersion: AppVersion ) : AnalyticsWrapper { override fun report(event: String) { if (!appVersion.debug) { reportToSolution(event) } else { log(event) } } internal fun reportToSolution(event: String) { performComplexTask() analytics.report(event) } internal fun log(event: String) { Log.v(“AnalyticsWrapper”, event) } } A B B C
43. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `report in release build should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() every { appVersion.debug } returns false val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) subject.report("test event") verify { subject.reportToSolution("test event") } } }
44. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `report in release build should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() every { appVersion.debug } returns false val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) subject.report("test event") verify { subject.reportToSolution("test event") } } }
45. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `report in release build should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() every { appVersion.debug } returns false val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) subject.report("test event") verify { subject.reportToSolution("test event") } } }
46. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `report in release build should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() every { appVersion.debug } returns false val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) subject.report("test event") verify { subject.reportToSolution("test event") } } }
47. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } verify { solution.report("test event") } } }
48. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } verify { solution.report("test event") } } }
49. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } verify { solution.report("test event") } } }
50. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } verify { solution.report("test event") } } }
51. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution, private val appVersion: AppVersion ) : AnalyticsWrapper { override fun report(event: String) { if (!appVersion.debug) { reportToSolution(event) } else { log(event) } } internal fun reportToSolution(event: String) { performComplexTask() analytics.report(event) } internal fun log(event: String) { Log.v(“AnalyticsWrapper”, event) } } A B B C
52. @rbusarow Mocking class AnalyticsWrapperImpl( private val analytics: AnalyticsSolution, private val appVersion: AppVersion ) : AnalyticsWrapper { override fun report(event: String) { if (!appVersion.debug) { reportToSolution(event) } else { log(event) } } internal fun reportToSolution(event: String) { performComplexTask() } internal fun log(event: String) { Log.v(“AnalyticsWrapper”, event) } } A B B ???
53. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } verify { solution.report("test event") } } } Fails
54. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `reportToSolution should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) every { subject.performComplexTask() } just runs subject.report("test event") verify { subject.performComplexTask() } } }
55. @rbusarow Mocking internal class AnalyticsWrapperImplTest { @Test fun `report in release build should delegate to AnalyticsSolution`() { val solution: AnalyticsSolution = mockk(relaxed = true) val appVersion: AppVersion = mockk() every { appVersion.debug } returns false val subject = spyk(AnalyticsWrapperImpl(solution, appVersion)) subject.report("test event") verify { subject.reportToSolution("test event") } } }
56. @rbusarow Verify is usually a code smell
57. @rbusarow use it as a last resort
58. @rbusarow class SomePresenter( val analyticsWrapper: AnalyticsWrapper ) { fun onImportantButtonClick() { analyticsWrapper.report("important click") } }
59. @rbusarow class SomePresenterTest { @Test fun `onImportantButtonClick should report to AnalyticsWrapper`() { val analyticsWrapper: AnalyticsWrapper = mockk(relaxed = true) val subject = SomePresenter(analyticsWrapper) subject.onImportantButtonClick() verify { analyticsWrapper.report("important click") } } }
60. @rbusarow class SomePresenterTest { @Test fun `onImportantButtonClick should report to AnalyticsWrapper`() { val analyticsWrapper: AnalyticsWrapper = mockk(relaxed = true) val subject = SomePresenter(analyticsWrapper) subject.onImportantButtonClick() verify { analyticsWrapper.report("important click") } } }
61. @rbusarow class SomePresenterTest { @Test fun `onImportantButtonClick should report to AnalyticsWrapper`() { val analyticsWrapper: AnalyticsWrapper = mockk(relaxed = true) val subject = SomePresenter(analyticsWrapper) subject.onImportantButtonClick() verify { analyticsWrapper.report("important click") } } }
62. @rbusarow interface AnalyticsWrapper { fun report(event: String) }
63. @rbusarow interface AnalyticsWrapper { fun report(event: String) } class FakeAnalyticsWrapper : AnalyticsWrapper { override fun report(event: String) { history.add(event) } }
64. @rbusarow interface AnalyticsWrapper { fun report(event: String) } class FakeAnalyticsWrapper : AnalyticsWrapper { val history = mutableListOf<String>() override fun report(event: String) { history.add(event) } fun reset() = history.clear() }
65. @rbusarow class SomePresenterTest { @Test fun `onImportantButtonClick should report to AnalyticsWrapper`() { val analyticsWrapper: AnalyticsWrapper = mockk(relaxed = true) val subject = SomePresenter(analyticsWrapper) subject.onImportantButtonClick() verify { analyticsWrapper.report("important click") } } }
66. @rbusarow class SomePresenterTest { @Test fun `onImportantButtonClick should report to AnalyticsWrapper`() { val analyticsWrapper = FakeAnalyticsWrapper() val subject = SomePresenter(analyticsWrapper) subject.onImportantButtonClick() analyticsWrapper.history shouldBe listOf("important click") } }
67. @rbusarow interface EventDao { fun getAll(): List<Event> fun getById(id: String): Event? fun insert(event: Event) }
68. @rbusarow class FakeEventDao : EventDao { val store = mutableMapOf<String, Event>() override fun getAll(): List<Event> = store.values.toList() override fun getById(id: String): Event? = store[id] override fun insert(event: Event) { store[event.id] = event } }
69. @rbusarow data class Event( val id: String, val message: String, val syncTimestamp: Long?, val source: String )
70. @rbusarow object FakeEvent { fun create( id: String = ID, message: String = MESSAGE, syncTimestamp: Long? = null, source: String = SOURCE ) = Event( id = id, message = message, syncTimestamp = syncTimestamp, source = source ) const val ID = "EVENT_ID" const val MESSAGE = "EVENT_MESSAGE" const val SOURCE = "EVENT_SOURCE" }
71. rbusarow Rick Busarow Slides speakerdeck.com/rbusarow/fakes-mocks-and-spies-oh-my KotlinTest github.com/kotlintest/kotlintest Kluent markusamshove.github.io/Kluent/ MockK mockk.io