Mocking Kotlin with MockK

Introduction to the mocking library MockK

Transcript

1. Mocking Kotlin With MockK
   Hadi Tok
   CitizenMe
   @hadi_tok
   

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2. Unit Testing
   

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3. Unit Testing
   ● Unit: Smallest testable component (function, class)
   ● Units are tested independently from each other
   ● Other units with dependencies are mocked or faked
   

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4. Unit Testing
   

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5. Testable Code
   ● Separations of Concerns
   ● Dependency injection
   ● Clean Code
   

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6. Stub
   ● Returning values without logic.
   ● Could return constant values or use a lookup table
   

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7. Fake
   ● Could have lightweight logic
   ● Cut corners for testing purposes so can’t be used in
   production
   

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8. Mock
   Northern mockingbird (Mimus polyglottos)
   

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9. Mock
   ● Not authentic or real, but without the intention to
   deceive.
   ● Imitates objects to specify behaviour explicitly and
   enables full control over the object.
   ● Usually backed with a library/framework
   

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10. Mocking
    ● What functions and variables return
    ● Check if the function calls and variable assignments are
    made with correct values
    

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11. MockK
    

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12. Why MockK
    ● Pure Kotlin
    ● Easy to use Domain Specific Language(DSL)
    ● Can also mock Java
    

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13. Sample
    

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14. data class User(val userId: String, val userName: String)
    

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15. data class User(val userId: String, val userName: String)
    interface UserApi {
    fun deleteUser(userId: String): Boolean
    }
    

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16. data class User(val userId: String, val userName: String)
    interface UserApi {
    fun deleteUser(userId: String): Boolean
    }
    class UserManager(private val userApi: UserApi) {
    fun deleteUser(user: User): Boolean {
    return userApi.deleteUser(user.userId)
    }
    }
    

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17. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    }
    

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18. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    }
    

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19. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    }
    

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20. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    }
    

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21. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    }
    

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22. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    }
    

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23. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    verify { userApi.deleteUser(userId) }
    }
    

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24. Argument Matching
    

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25. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    verify { userApi.deleteUser(userId) }
    }
    

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26. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    verify { userApi.deleteUser(match { it.startsWith("12") }) }
    }
    

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27. @Test
    fun basicTest() {
    val userApi: UserApi = mockk()
    val userManager = UserManager(userApi)
    val userId = "123"
    val user: User = mockk()
    every { user.userId } returns userId
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    verify { userApi.deleteUser(any()) }
    }
    

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28. Matchers
    ● more(), less(), range()
    ● eq(), neq(), refEq(), cmpEq()
    ● isNull(), isNull(inverse=true)
    ● match{}, matchNullable{}
    

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29. Annotations
    

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30. @MockK
    lateinit var userApi: UserApi
    @MockK
    lateinit var user: User
    val userId = “123"
    lateinit var userManager:UserManager
    

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31. @MockK
    lateinit var userApi: UserApi
    @MockK
    lateinit var user: User
    val userId = “123"
    lateinit var userManager:UserManager
    @Before
    fun initTests() {
    MockKAnnotations.init(this)
    userManager = UserManager(userApi)
    every { user.userId } returns userId
    }
    

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32. @Test
    fun basicTest() {
    every { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    verify { userApi.deleteUser(userId) }
    }
    

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33. Object Mock
    

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34. object Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    

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35. object Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun objectMock() {
    val result = Calculator.add(1, 2)
    assert(result).toBe(3)
    }
    

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36. object Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun objectMock() {
    val result = Calculator.add(1, 2)
    assert(result).toBe(3)
    mockkObject(Calculator)
    every { Calculator.add(1, 2) } returns 42
    }
    

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37. object Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun objectMock() {
    val result = Calculator.add(1, 2)
    assert(result).toBe(3)
    mockkObject(Calculator)
    every { Calculator.add(1, 2) } returns 42
    }
    

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38. object Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun objectMock() {
    val result = Calculator.add(1, 2)
    assert(result).toBe(3)
    mockkObject(Calculator)
    every { Calculator.add(1, 2) } returns 41
    val mockedResult = Calculator.add(1, 2)
    assert(mockedResult).toBe(42)
    }
    

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39. Static Mock
    

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40. public class CalculatorStatic {
    static int add(int first, int second){
    return first+second;
    }
    }
    

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41. @Test
    fun staticMock() {
    val result = CalculatorStatic.add(1, 2)
    assert(result).toBe(3)
    }
    

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42. @Test
    fun staticMock() {
    val result = CalculatorStatic.add(1, 2)
    assert(result).toBe(3)
    mockkStatic(CalculatorStatic::class)
    }
    

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43. @Test
    fun staticMock() {
    val result = CalculatorStatic.add(1, 2)
    assert(result).toBe(3)
    mockkStatic(CalculatorStatic::class)
    every { CalculatorStatic.add(1, 2) } returns 42
    }
    

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44. @Test
    fun staticMock() {
    val result = CalculatorStatic.add(1, 2)
    assert(result).toBe(3)
    mockkStatic(CalculatorStatic::class)
    every { CalculatorStatic.add(1, 2) } returns 42
    val mockedResult = CalculatorStatic.add(1, 2)
    }
    

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45. @Test
    fun staticMock() {
    val result = CalculatorStatic.add(1, 2)
    assert(result).toBe(3)
    mockkStatic(CalculatorStatic::class)
    every { CalculatorStatic.add(1, 2) } returns 42
    val mockedResult = CalculatorStatic.add(1, 2)
    assert(mockedResult).toBe(42)
    }
    

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46. Argument Capturing
    

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47. class Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    

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48. class Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun argumentCapturing() {
    val calculator:Calculator = mockk()
    }
    

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49. class Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun argumentCapturing() {
    val calculator:Calculator = mockk()
    every { calculator.add(any(), any()) } answers {
    firstArg() + secondArg()
    }
    }
    

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50. class Calculator {
    fun add(first: Int, second: Int) = first + second
    }
    @Test
    fun argumentCapturing() {
    val calculator:Calculator = mockk()
    every { calculator.add(any(), any()) } answers {
    firstArg() + secondArg()
    }
    val mockedResult = calculator.add(1, 2)
    assert(mockedResult).toBe(3)
    }
    

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51. Coroutines
    

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52. data class User(val userId: String, val userName: String)
    

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53. data class User(val userId: String, val userName: String)
    interface UserApi {
    suspend fun deleteUser(userId: String): Boolean
    }
    

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54. data class User(val userId: String, val userName: String)
    interface UserApi {
    suspend fun deleteUser(userId: String): Boolean
    }
    class UserManager(private val userApi: UserApi) {
    suspend fun deleteUser(user: User): Boolean {
    return userApi.deleteUser(user.userId)
    }
    }
    

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55. @MockK
    lateinit var userApi: UserApi
    @MockK
    lateinit var user: User
    val userId = “123"
    lateinit var userManager:UserManager
    @Before
    fun initTests() {
    MockKAnnotations.init(this)
    userManager = UserManager(userApi)
    every { user.userId } returns userId
    }
    

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56. @Test
    fun basicTest() = runBlocking {
    }
    

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57. @Test
    fun basicTest() = runBlocking {
    every { user.userId } returns userId
    }
    

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58. @Test
    fun basicTest() = runBlocking {
    every { user.userId } returns userId
    coEvery { userApi.deleteUser(userId) } returns true
    }
    

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59. @Test
    fun basicTest() = runBlocking {
    every { user.userId } returns userId
    coEvery { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    }
    

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60. @Test
    fun basicTest() = runBlocking {
    every { user.userId } returns userId
    coEvery { userApi.deleteUser(userId) } returns true
    val result = userManager.deleteUser(user)
    assert(result).toBe(true)
    coVerify { userApi.deleteUser(userId) }
    }
    

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61. Other features
    ● Spy
    ● Constructor mock
    ● Extension function mock
    ● Enumeration mock
    

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62. Limitations
    ● final static
    ● inline functions
    

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63. Resources
    ● https://mockk.io/
    ● Mocking is not rocket science: Basics:
    https://blog.kotlin-academy.com/mocking-is-not-rocke
    t-science-basics-ae55d0aadf2b
    

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64. Unit tests without integration tests (Obligatory gif)
    

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65. Questions?
    

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66. Hadi Tok, CitizenMe
    @hadi_tok
    Thank you!
    

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