Pragmatic Testing

(given at Droidcon Italy 2018 and Android Makers 2018)

You open a pull request only to find that some tests are now failing. What goes through your mind?

Did I break something? Do I need to update the tests? Just what is that test testing anyway?

Ideally, #2 would almost never be the case, as rewriting a test usually means it's lost the regression testing value of its original form. How can we get there though? There’s no one right way to write tests, and it’s surprisingly easy to fall into the trap of writing change tests. There are good patterns you can leverage to scale them and maximize their long term value. This talk will detail simple patterns you can follow for healthy, pragmatic testing with a focus on test design, correctness, and how these values can translate into better overall API design of your code.

Transcript

1. Pragmatic
   Testing
   Zac Sweers - Uber
   @pandanomic
   

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2. Testing?
   

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3. Testing!
   

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4. @Test
   

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5. @Test
   

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6. Pragmatic
   Testing
   

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7. Pragmatic?
   Testing
   

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8. Goals ⚽
   

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9. Non-Goals
   

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10. Non-Goals
    • Convince you testing is worthwhile
    

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11. Non-Goals
    • Convince you testing is worthwhile
    • UI Testing (Espresso, layouts, etc)
    

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12. Non-Goals
    • Convince you testing is worthwhile
    • UI Testing (Espresso, layouts, etc)
    • Knock specific libraries
    

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14. Boundaries
    

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15. Calculator
    

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16. Calculator
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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17. Calculator
    InputManager
    DisplayManager
    CPU
    RAM
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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18. InputManager
    DisplayManager
    CPU
    RAM
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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19. InputManager
    DisplayManager
    CPU
    RAM
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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20. InputManager
    DisplayManager
    CPU
    RAM
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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21. InputManager
    DisplayManager
    CPU
    RAM
    add()
    subtract()
    multiply()
    divide()
    equal()
    clear()
    

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22. InputManager DisplayManager
    CPU RAM
    

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23. InputManager DisplayManager
    CPU RAM
    

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24. @Test
    fun testAdd() {
    }a
    InputManager DisplayManager
    CPU RAM
    

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25. @Test
    fun testAdd() {
    val calculator = Calculator()
    }a
    InputManager DisplayManager
    CPU RAM
    

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26. @Test
    fun testAdd() {
    val cpu = mock(CPU::class.java)
    val calculator = Calculator()
    }a
    InputManager DisplayManager
    CPU RAM
    

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27. @Test
    fun testAdd() {
    val cpu = mock(CPU::class.java)
    val ram = mock(RAM::class.java)
    val calculator = Calculator()
    }a
    InputManager DisplayManager
    CPU RAM
    

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28. @Test
    fun testAdd() {
    val cpu = mock(CPU::class.java)
    val ram = mock(RAM::class.java)
    val display = mock(DisplayManager::class.java)
    val calculator = Calculator()
    }a
    InputManager DisplayManager
    CPU RAM
    

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29. @Test
    fun testAdd() {
    val cpu = mock(CPU::class.java)
    val ram = mock(RAM::class.java)
    val display = mock(DisplayManager::class.java)
    val input = mock(InputManager::class.java)
    val calculator = Calculator()
    }a
    InputManager DisplayManager
    CPU RAM
    

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30. @Test
    fun testAdd() {
    val cpu = mock(CPU::class.java)
    val ram = mock(RAM::class.java)
    val display = mock(DisplayManager::class.java)
    val input = mock(InputManager::class.java)
    val calculator = Calculator(cpu, ram, display, input)
    }a
    InputManager DisplayManager
    CPU RAM
    

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31. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    }a
    InputManager DisplayManager
    CPU RAM
    

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32. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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33. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    }a
    InputManager DisplayManager
    CPU RAM
    

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34. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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35. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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36. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    }a
    InputManager DisplayManager
    CPU RAM
    

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37. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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38. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    }a
    InputManager DisplayManager
    CPU RAM
    

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39. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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40. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    }a
    

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41. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    }a
    

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42. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    }a
    

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43. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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44. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    input.add(2, 2)
    verify(cpu).setRam(ram)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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45. @Test
    fun testAdd() {
    input.add(2, 2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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46. @Test
    fun testAdd() {
    input.add(2, 2)
    }a
    registerInputListener(listener: Listener)
    InputManager DisplayManager
    CPU RAM
    

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47. val captor = ArgumentCaptor.forClass(Listener::class.java)
    InputManager DisplayManager
    CPU RAM
    

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48. val captor = ArgumentCaptor.forClass(Listener::class.java)
    verify(input).registerInputListener(captor.capture())
    InputManager DisplayManager
    CPU RAM
    

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49. val captor = ArgumentCaptor.forClass(Listener::class.java)
    verify(input).registerInputListener(captor.capture())
    val listener = captor.value
    InputManager DisplayManager
    CPU RAM
    

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50. @Test
    fun testAdd() {
    val captor = ArgumentCaptor.forClass(Listener::class.java)
    verify(input).registerInputListener(captor.capture())
    val listener = captor.value
    input.add(2, 2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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51. @Test
    fun testAdd() {
    // Captor stuff
    input.add(2, 2)
    }a
    InputManager DisplayManager
    CPU RAM
    

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52. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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53. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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54. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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55. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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56. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    

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57. @Test
    fun testAdd() {
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    InputManager DisplayManager
    CPU RAM
    

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58. @Test
    fun testAdd() {
    verify(cpu).calculateSum(2, 2) // Actually 0
    verify(display).displayResult(4)
    }a
    InputManager DisplayManager
    CPU RAM
    

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59. @Test
    fun testAdd() {
    when(cpu.calculateSum(2, 2)).thenReturn(4)
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    InputManager DisplayManager
    CPU RAM
    

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60. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    when(cpu.calculateSum(2, 2)).thenReturn(4)
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    

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61. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    when(cpu.calculateSum(2, 2)).thenReturn(4)
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    

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62. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    verify(cpu).setRam(ram)
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    listener.onNewInput("+")
    verify(input).onInputReceived("+")
    verify(ram).storeInRAM(2)
    verify(cpu).loadInputToCpu("+")
    listener.onNewInput(2)
    verify(input).onInputReceived(2)
    verify(cpu).loadInputToCpu(2)
    verify(ram).loadFromRam()
    when(cpu.calculateSum(2, 2)).thenReturn(4)
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    

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63. @Test
    fun testAdd() {
    // Mocks...
    val calculator = Calculator(cpu, ram, display, input)
    // Captor stuff...
    input.add(2, 2)
    listener.onNewInput(2)
    listener.onNewInput("+")
    listener.onNewInput(2)
    when(cpu.calculateSum(2, 2)).thenReturn(4)
    verify(cpu).calculateSum(2, 2)
    verify(display).displayResult(4)
    }a
    InputManager DisplayManager
    CPU RAM
    

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64. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display, input)
    }a
    

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65. InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display, input)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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66. InputManager DisplayManager
    CPU RAM
    InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display, input)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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67. DisplayManager
    CPU RAM
    InputManager DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display, input)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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68. DisplayManager
    CPU RAM DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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69. DisplayManager
    RAM DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(cpu, ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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70. DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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71. @Test
    fun testAdd() {
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    DisplayManager
    CPU RAM DisplayManager
    CPU RAM
    

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72. DisplayManager
    CPU DisplayManager
    CPU RAM
    @Test
    fun testAdd() {
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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73. RAM
    

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74. RAM
    interface RAMa{
    afunastoreInRAM(key:aString,avalue:aT)
    afunaloadFromRam(key:aString):aT?
    }
    

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75. class InMemoryRAM : RAMa{
    private val store = mutableMapOf()
    override afunastoreInRAM(key:aString,avalue:aT) {
    return store[key] = value
    }
    override afunaloadFromRam(key:aString):aT? {
    return store[key]
    }
    }
    

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76. InMemoryRAM
    

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77. DisplayManager
    CPU InMemoryRAM
    @Test
    fun testAdd() {
    val ram = mock(RAM::class.java)
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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78. DisplayManager
    CPU InMemoryRAM
    @Test
    fun testAdd() {
    val ram = InMemoryRAM()
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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79. CPU DisplayManager
    CPU
    @Test
    fun testAdd() {
    val ram = InMemoryRAM()
    val calculator = Calculator(CPU(), ram, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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80. CPU DisplayManager
    CPU
    @Test
    fun testAdd() {
    val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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81. CPU
    CPU DisplayManager
    @Test
    fun testAdd() {
    val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu, display)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    DisplayManager
    

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82. CPU
    CPU DisplayManager
    verify(display).displayResult(4)
    DisplayManager
    

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83. CPU
    CPU DisplayManager
    verify(display).displayResult(4)
    assertThat(display.getCurrentResult()).isEqualTo(4)
    DisplayManager
    

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84. CPU
    CPU DisplayManager
    verify(display).displayResult(4)
    assertThat(display.getCurrentResult()).isEqualTo(4)
    assertThat(display.recordedResults[0]).isEqualTo(4)
    DisplayManager
    

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85. CPU
    CPU
    val resultHandler = RecordingResultHandler()
    // Calc
    assertThat(resultHandler.results[0]).isEqualTo(4)
    ResultHandler
    

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86. CPU ResultHandler
    CPU
    @Test
    fun testAdd() {
    val cpu = CPU(InMemoryRAM())
    val resultHandler = RecordingResultHandler()
    val calculator = Calculator(cpu, resultHandler)
    calculator.add(2, 2)
    assertThat(resultHandler.results[0]).isEqualTo(4)
    }a
    

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87. CPU
    @Test
    fun testAdd() {
    val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu)
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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88. val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu)
    @Test
    fun testAdd() {
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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89. val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu)
    @Testa
    fun testAdd() {
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    @Testb
    fun testSub() {
    assertThat(calculator.subtract(2, 2)).isEqualTo(0)
    }b
    @Testc
    fun testMultiply() {
    assertThat(calculator.multiply(2, 2)).isEqualTo(4)
    }c
    

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90. val cpu = CPU(InMemoryRAM())
    val calculator = Calculator(cpu)
    @Testa
    fun testAdd() {
    assertThat(calculator.add(2, 2)).isEqualTo(4)
    }a
    

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91. val cpu = CPU(InMemoryRAM())
    val resultHandler = RecordingResultHandler()
    val calculator = Calculator(cpu, resultHandler)
    @Test
    fun testAdd() {
    calculator.add(2, 2)
    calculator.add(2, 3)
    calculator.add(2, -1)
    assertThat(resultHandler.results)
    .containsExactly(4, 5, 1)
    }a
    

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92. Failure
    

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93. @Test
    fun foo() {
    try {
    foo.bar()
    } catch (e: Exception) {
    // Expected
    }
    }a
    

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94. @Test(expected = Exception::class)
    fun foo() {
    foo.bar()
    }a
    

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95. @Test(expected = ExpectedException::class)
    fun foo() {
    foo.bar()
    }a
    

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96. @Test()
    fun foo() {
    try {
    foo.bar()
    } catch (e: ExpectedException) {
    assertThat(e)
    .hasMessageThat()
    .contains("Oh no")
    }b
    }a
    

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97. @Test()
    fun foo() {
    try {
    foo.bar()
    throw AssertionError("No")
    } catch (e: ExpectedException) {
    assertThat(e)
    .hasMessageThat()
    .contains("Oh no")
    }b
    }a
    

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98. RxJava
    

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99. @Test()
    fun rx() {
    Observable.error()
    .subscribe()
    }a
    

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100. @Test()
     fun rx() {
     Observable.error()
     .subscribe()
     }a
     

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101. throw error
     

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102. // throw error
     Thread currentThread = Thread.currentThread();
     UncaughtExceptionHandler handler
     = currentThread.getUncaughtExceptionHandler();
     handler.uncaughtException(currentThread, error);
     

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103. // throw error
     Thread currentThread = Thread.currentThread();
     UncaughtExceptionHandler handler
     = currentThread.getUncaughtExceptionHandler();
     handler.uncaughtException(currentThread, error);
     https://github.com/uber/AutoDispose/blob/master/autodispose/src/test/java/com/uber/
     autodispose/RxErrorsRule.java
     

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104. TestObserver
     

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105. TestObserver
     Observable.just(1)
     .test()
     

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106. TestObserver
     Observable.just(1)
     .test()
     .assertValue(...)
     

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107. TestObserver
     Observable.just(1)
     .test()
     .assertValue(...)
     .assertError(...)
     

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108. TestObserver
     Observer o = mock(Observer::class.java)
     Observable.just(1)
     .subscribe(o)
     verify(o).onNext(...)
     verify(o).onError(...)
     

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109. TestObserver
     Observable.just(1)
     .test()
     .assertValue(...)
     .assertError(...)
     .awaitDone(...)
     

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110. Some others
     quickly because ⏰
     

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111. What about my
     architecture?
     

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112. class Calculator(val cpu: CPU,
     val resultHandler: ResultHandler,
     val inputManager: InputManager)
     

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113. class CalculatorPresenter(val cpu: CPU,
     val resultHandler: ResultHandler,
     val inputManager: InputManager)
     

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114. class CalculatorPresenter(val cpu: CPU,
     val resultHandler: ResultHandler,
     val inputManager: InputManager)
     Courtesy of Nick Butcher (@crafty)
     

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115. class CalculatorPresenter(val cpu: CPU,
     val resultHandler: ResultHandler,
     val inputManager: InputManager)
     0.0
     7 8 9
     4 5 6
     1 2 3
     C 0 ⏎
     

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116. class CurrentValueView : ResultHandler
     0.0
     7 8 9
     4 5 6
     1 2 3
     C 0 ⏎
     

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117. class NumberInputManager : InputManager
     class CurrentValueView : ResultHandler
     0.0
     7 8 9
     4 5 6
     1 2 3
     C 0 ⏎
     

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118. class NumberInputManager : InputManager
     class CurrentValueView : ResultHandler
     0.0
     7 8 9
     4 5 6
     1 2 3
     C 0 ⏎
     class ImeInputManager : InputManager
     

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119. class NumberInputManager : InputManager
     class CurrentValueView : ResultHandler
     7 8 9
     4 5 6
     1 2 3
     C 0 ⏎
     0.0
     

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120. What about DI?
     

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121. class MainActivity : Activity {
     @Inject lateinit var foo: Foo
     @Inject lateinit var bar: Bar
     }
     

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122. @Test
     fun testActivity() {
     val activity = ...
     activity.foo = TestFoo()
     activity.bar = MockBar()
     }
     

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123. @Test
     fun testActivity() {
     val activity = MainActivityTestHelper.create(
     TestFoo(),
     MockBar()
     )a
     }b
     

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124. @Test
     fun testActivity() {
     val activity = MainActivityTestHelper.create(
     TestFoo(),
     MockBar()
     )a
     }b
     RIBS: https://github.com/uber/RIBs/blob/master/android/libraries/rib-
     compiler-test/src/main/java/com/uber/rib/compiler/
     InteractorTestGenerator.java
     Injection Helper: https://github.com/dinosaurwithakatana/injection-
     helper
     

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125. What about
     state?
     

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126. State machines!
     

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127. In short
     

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128. Value is the
     boundary
     

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129. Value is the
     boundary
     assertThat(calculator.add(2, 2)).isEqualTo(4)
     assertThat(resultHandler.results[0]).isEqualTo(4)
     Observable.just(1)
     .test()
     .assertValue(...)
     .assertError(...)
     .awaitDone(...)
     

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130. Fakes are worth
     writing
     

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131. Fakes are worth
     writing
     class InMemoryRAM : RAM {
     private val store = mutableMapOf()
     override fun storeInRAM(key: String, value: T) {
     return store[key] = value
     }
     override fun loadFromRam(key: String): T? {
     return store[key]
     }
     }
     

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132. Ship your fakes
     

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133. Ship your fakes
     fun test(): TestObserver
     TestScopeProvider
     Room.inMemoryDatabaseBuilder(...)
     

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134. Tests should test
     the public API
     

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135. Tests should test
     the public API
     Semver your
     tests!
     

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136. Test are prod
     code
     

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137. Failures should
     be designed for
     

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138. Failures should
     be designed for
     throw AssertionError("Should have crashed before this")
     catch (e: ExpectedException) {
     assertThat(e).isWhatWeExpected()
     }
     @Rule val errorsRule = RxErrorsRule()
     

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139. More than one
     right way
     

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140. Keep it simple.
     

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141. Keep it pragmatic.
     

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142. Further reading
     • Boundaries: https://
     www.destroyallsoftware.com/talks/boundaries
     • Square libraries
     • RxJava
     • AutoDispose
     

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143. Fini, merci!
     Zac Sweers - Uber
     @pandanomic
     

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