Write awesome unit tests

Slides from my talk at Devoxx 2018
Video: https://www.youtube.com/watch?v=F8Gc8Nwf0yk

While there are plenty of resources about writing awesome code, the same doesn't quite exist for tests. So how do you write great unit tests? And how do you ensure failures are easy to fix? What are the best practices? And most importantly what are the pitfalls to look out for?

If you're already comfortable writing tests, come level up your testing skills with deep insights into the "Why" and "How" of fundamental testing principles. You will learn:

- What three criteria make tests awesome
- What to test and what not to test
- Why you should optimise tests for failure
- How many tests you should write per method
- How to test literally everything
- What is code coverage and why it can be deceiving
- How to use AssertJ to make test super readable
- What TDD is and what its benefit is
- ...

Transcript

1. @MOLSJEROEN
   WRITE AWESOME
   UNIT TESTS
   

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2. @MOLSJEROEN
   @MOLSJEROEN
   

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3. @MOLSJEROEN
   CORE PRINCIPLES
   THREE GROUND RULES
   CODE COVERAGE
   TEST DRIVEN DEVELOPMENT
   TESTING MYTHS
   TEST VS PRODUCTION CODE
   TIPS
   

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4. CORE PRINCIPLES
   

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5. @MOLSJEROEN
   WHY DO WE WRITE TESTS?
   Proof of working code
   Safeguard that code keeps on working
   Documentation
   Enables refactoring
   Release faster
   Easiest form of testing
   …
   

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6. WE WRITE TESTS TO RUN THEM
   

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7. @MOLSJEROEN
   TESTING IS A LONG TERM COMMITMENT
   Fix failing test
   Remove obsolete tests
   Refactor existing tests
   Upgrade test frameworks
   Fix bugs in tests
   …
   

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8. TESTS ARE PRODUCTION C0DE
   

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9. @MOLSJEROEN
   TESTS REQUIRE INFRASTRUCTURE
   CI server to run tests
   Dependency injection framework
   Tools to analyze code coverage
   Slack integration when tests fail
   Build command to run tests
   Hardware to run tests on
   …
   

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10. OPTIMIZE TESTS FOR FAILURE
    

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11. THREE GROUND RULES
    

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12. @MOLSJEROEN
    1 - RUN LUDICROUSLY FAST
    Safety net against regression
    Detect bugs early and cheaply
    Rapid feedback loop is required
    Run tests on every change
    

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13. @MOLSJEROEN
    

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14. @MOLSJEROEN
    2 - SMALL AND FOCUSSED
    Only few lines of code
    Clear structure: Assert/Act/Arrange
    Only one failing test for each bug
    Test name indicates the problem
    

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15. @MOLSJEROEN
    @Test
    fun `login should fail with wrong password`() {
    // Test code
    }
    

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16. @MOLSJEROEN
    3 - 100% RELIABLE
    Drop everything to fix failure
    Reason must be obvious
    Failures should be rare
    Correlation with modified code
    “Magical rerun” drives developers mad
    Lose of trust in safety net
    

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17. @MOLSJEROEN
    @Test
    fun `should properly format time`() {
    val expectedTime = FORMAT.format(Date())
    val formattedTime = TimeFormatter().currentFormattedTime
    assertEquals(expectedTime, formattedTime)
    }
    companion object {
    private val FORMAT = SimpleDateFormat("HH:mm:ss:SSS")
    }
    

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18. @MOLSJEROEN
    @Test
    fun `should properly format time`() {
    val expectedTime = FORMAT.format(Date())
    val formattedTime = TimeFormatter().currentFormattedTime
    assertEquals(expectedTime, formattedTime)
    }
    companion object {
    private val FORMAT = SimpleDateFormat("HH:mm:ss:SSS")
    }
    

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19. @MOLSJEROEN
    @Test
    fun `should properly format time`() {
    val now = Date()
    val expectedTime = FORMAT.format(now)
    val formattedTime = TimeFormatter().currentFormattedTime(now)
    assertEquals(expectedTime, formattedTime)
    }
    companion object {
    private val FORMAT = SimpleDateFormat("HH:mm:ss:SSS")
    }
    

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20. CODE COVERAGE
    

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21. IF YOUR APP HAS 100% CODE COVERAGE,
    CAN IT STILL HAVE BUGS?
    

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22. @MOLSJEROEN
    100% APP COVERAGE
    Does not mean app is bug free!
    UI inconsistencies
    Interaction between classes
    Interaction with external services
    ….
    

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23. IF A CLASS HAS 100% CODE COVERAGE,
    CAN THAT STILL HAVE BUGS?
    

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24. @MOLSJEROEN
    class Calculator {
    fun sum(a: Int, b: Int): Int {
    return a + b
    }
    }
    

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25. @MOLSJEROEN
    class Calculator {
    fun sum(a: Int, b: Int): Int {
    return a + b
    }
    }
    @Test
    fun `sum of one and three is four`() {
    val result = Calculator().sum(1,3)
    assertEquals(4, result)
    }
    

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26. @MOLSJEROEN
    class Calculator {
    fun sum(a: Int, b: Int): Int {
    return a + b
    }
    }
    @Test
    fun `sum of one and three is four`() {
    val result = Calculator().sum(1,3)
    }
    

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27. @MOLSJEROEN
    class Calculator {
    fun sum(a: Int, b: Int): Int {
    return 4
    }
    }
    @Test
    fun `sum of one and three is four`() {
    val result = Calculator().sum(1,3)
    assertEquals(4, result)
    }
    

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28. @MOLSJEROEN
    100% COVERAGE
    Doesn’t mean anything
    Agnostic about quality of the tests
    Unaware of functionality coverage
    Not even check for asserts
    

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29. @MOLSJEROEN
    Coverage
    Effort
    

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30. @MOLSJEROEN
    

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31. TEST DRIVEN DEVELOPMENT
    

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32. @MOLSJEROEN
    WRITE TESTS BEFORE OR AFTER CODE
    Doesn’t matter!
    But, writing before:
    …guarantees test would fail
    …reduces manual testing
    …is easier
    …forces you to think better about requirements
    …helps split a problem in smaller parts
    

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33. @MOLSJEROEN
    TDD - WHAT
    (Extreme) way of working
    Flow:
    1. Write no code except to make a test pass or failing test
    2. Write minimum code to make test fail
    3. Write minimum code to make test pass
    

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34. @MOLSJEROEN
    Green
    Red
    Refactor
    

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35. @MOLSJEROEN
    TEST DRIVEN
    … Development
    … Design
    … Divide and conquer
    … Documentation
    … DevOps
    … Determination
    … Dream
    

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36. @MOLSJEROEN
    class CalculatorTest {
    }
    

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37. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `can instantiate`() {
    Calculator()
    }
    }
    

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38. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `can instantiate`() {
    Calculator()
    }
    }
    class Calculator {
    }
    

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39. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `can instantiate`() {
    Calculator()
    }
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    }
    class Calculator {
    }
    

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40. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `can instantiate`() {
    Calculator()
    }
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    TODO("not implemented")
    }
    }
    

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41. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `can instantiate`() {
    Calculator()
    }
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return 4
    }
    }
    

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42. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return 4
    }
    }
    

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43. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    @Test
    fun `two plus three is five`() {
    Calculator().sum(2, 3)
    }
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return 4
    }
    }
    

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44. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    @Test
    fun `two plus three is five`() {
    Calculator().sum(2, 3)
    }
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return if (a == 1) 4 else 5
    }
    }
    

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45. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    @Test
    fun `two plus three is five`() {
    Calculator().sum(2, 3)
    }
    @Test
    fun `three plus three is six`() {
    Calculator().sum(3, 3)
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return if (a == 1) 4 else 5
    }
    }
    

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46. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    @Test
    fun `two plus three is five`() {
    Calculator().sum(2, 3)
    }
    @Test
    fun `three plus three is six`() {
    Calculator().sum(3, 3)
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return if (a == 1) 4
    else if (a == 2) 5
    else 6
    }
    }
    

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47. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun `one plus three is four`() {
    Calculator().sum(1, 3)
    }
    @Test
    fun `two plus three is five`() {
    Calculator().sum(2, 3)
    }
    @Test
    fun `three plus three is six`() {
    Calculator().sum(3, 3)
    }
    class Calculator {
    fun sum(a: Int, b: Int) : Int {
    return a + b
    }
    }
    

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48. TESTING MYTHS
    

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49. TESTING SLOWS DOWN DEVELOPMENT
    

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50. TESTING IS HARD
    

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51. TEST CODE IS NOT PRODUCTION CODE
    

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52. SIMPLE CODE SHOULDN’T BE TESTED
    

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53. TESTING NEGATIVELY IMPACTS THE
    PRODUCTION CODE
    

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54. EVERYTHING SHOULD BE TESTED
    

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55. TEST VS PRODUCTION CODE
    

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56. @MOLSJEROEN
    // Instrumented test, run on Android device.
    @RunWith(AndroidJUnit4::class)
    class CalculatorTest : TestCase() {
    fun test_sumShouldAddNumbers() {
    val sum = Calculator().sum(1, 2)
    assertThat(sum).isEqualTo(3)
    }
    }
    

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57. @MOLSJEROEN
    // Instrumented test, run on Android device.
    @RunWith(AndroidJUnit4::class)
    class CalculatorTest : TestCase() {
    fun test_sumShouldAddNumbers() {
    val sum = Calculator().sum(1, 2)
    assertThat(sum).isEqualTo(3)
    }
    }
    

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58. @MOLSJEROEN
    // Instrumented test, run on Android device.
    @RunWith(AndroidJUnit4::class)
    class CalculatorTest {
    @Test
    fun sumShouldAddNumbers() {
    val sum = Calculator().sum(1, 2)
    assertThat(sum).isEqualTo(3)
    }
    }
    

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59. @MOLSJEROEN
    // Instrumented test, run on Android device.
    @RunWith(AndroidJUnit4::class)
    class CalculatorTest {
    @Test
    fun sumShouldAddNumbers() {
    val sum = Calculator().sum(1, 2)
    assertThat(sum).isEqualTo(3)
    }
    }
    

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60. @MOLSJEROEN
    class CalculatorTest {
    @Test
    fun sumShouldAddNumbers() {
    val sum = Calculator().sum(1, 2)
    assertThat(sum).isEqualTo(3)
    }
    }
    

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61. USE JUNIT 4 SYNTAX
    

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62. @MOLSJEROEN
    class WebServiceTest {
    lateinit var webService: WebService
    @Before
    fun setUp() {
    webService = WebServiceTestHelper.createWebService()
    }
    @Test
    fun loginHasFailed() {
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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63. @MOLSJEROEN
    class WebServiceTest {
    lateinit var webService: WebService
    @Before
    fun setUp() {
    webService = WebServiceTestHelper.createWebService()
    }
    @Test
    fun loginHasFailed() {
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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64. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    var webService = WebServiceTestHelper.createWebService()
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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65. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    var webService = WebServiceTestHelper.createWebService()
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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66. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    var webService = WebService()
    webService.setUserCredentials("email@google.com", “wrong_pwd”)
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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67. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    var webService = WebService()
    webService.setUserCredentials("email@google.com", “wrong_pwd”)
    val result = webService.login()
    checkLoginFailed(result)
    }
    }
    

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68. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    var webService = WebService()
    webService.setUserCredentials("email@google.com", “wrong_pwd”)
    val result = webService.login()
    assertThat(result.isSuccess).isFalse()
    }
    }
    

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69. KEEP READER IN TEST
    

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70. @MOLSJEROEN
    internal class CalculatorTest {
    @Mock private lateinit var calculator : Calculator
    /* Test that perimeter is calculated correctly */
    @Test
    internal fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    private const val WIDTH = 5
    private const val HEIGHT = 10
    }
    

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71. @MOLSJEROEN
    internal class CalculatorTest {
    @Mock private lateinit var calculator : Calculator
    /* Test that perimeter is calculated correctly */
    @Test
    internal fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    private const val WIDTH = 5
    private const val HEIGHT = 10
    }
    

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72. @MOLSJEROEN
    internal class CalculatorTest {
    @Mock private lateinit var calculator : Calculator
    @Test
    internal fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    private const val WIDTH = 5
    private const val HEIGHT = 10
    }
    

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73. @MOLSJEROEN
    internal class CalculatorTest {
    @Mock private lateinit var calculator : Calculator
    @Test
    internal fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    private const val WIDTH = 5
    private const val HEIGHT = 10
    }
    

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74. @MOLSJEROEN
    class CalculatorTest {
    @Mock lateinit var calculator : Calculator
    @Test
    fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    const val WIDTH = 5
    const val HEIGHT = 10
    }
    

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75. @MOLSJEROEN
    class CalculatorTest {
    @Mock lateinit var calculator : Calculator
    @Test
    fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(WIDTH, HEIGHT)
    assertThat(circumference).isEqualTo(30)
    }
    companion object {
    const val WIDTH = 5
    const val HEIGHT = 10
    }
    

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76. @MOLSJEROEN
    class CalculatorTest {
    @Mock lateinit var calculator : Calculator
    @Test
    fun calculatePerimeterOfRectangle() {
    val geoCalculator = GeometryCalculator(calculator)
    val circumference = geoCalculator.perimeter(5, 10)
    assertThat(circumference).isEqualTo(30)
    }
    }
    

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77. NO CLUTTER
    

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78. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.isSuccess).isFalse()
    assertThat(result.user).isNull()
    }
    }
    

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79. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.isSuccess).isFalse()
    assertThat(result.user).isNull()
    }
    }
    

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80. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.user).isNull()
    }
    }
    

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81. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.user).isNull()
    }
    }
    

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82. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.user).isNull()
    }
    }
    

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83. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun loginHasFailed() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.user).isNull()
    }
    }
    

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84. @MOLSJEROEN
    class WebServiceTest {
    @Test
    fun `user is null when login fails`() {
    val webService = WebService()
    webService.setUserCredentials("email@google.com", "wrong_pwd")
    val result = webService.login()
    assertThat(result.user).isNull()
    }
    }
    

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85. OPTIMIZE TEST FOR FAILURE
    

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86. @MOLSJEROEN
    DO REPEAT YOURSELF
    USE MAGIC INTS AND STRINGS
    NO ENCAPSULATION
    DON’T LAYER TEST CLASSES
    LONG TEST METHOD NAMES
    

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87. TIPS
    

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88. @MOLSJEROEN
    TESTING UI
    View ViewModel Repository
    LiveData
    

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89. @MOLSJEROEN
    assertEquals(expected, actual)
    assertNull(actual)
    assertNotNull(actual)
    assertTrue(condition)
    assertFalse(condition)
    assertSame(expected, actual)
    assertNotSame(expected, actual)
    ASSERTJ
    

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90. @MOLSJEROEN
    assertEquals(expected, actual)
    assertNull(actual)
    assertNotNull(actual)
    assertTrue(condition)
    assertFalse(condition)
    assertSame(expected, actual)
    assertNotSame(expected, actual)
    assertThat(actual).isEqualTo(…)
    assertThat(actual).isNull()
    assertThat(actual).isNotNull()
    assertThat(condition).isTrue()
    assertThat(condition).isFalse()
    assertThat(actual).isSameAs(…)
    assertThat(actual).isNotSameAs(…)
    ASSERTJ
    

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91. @MOLSJEROEN
    assertThat(number).isGreaterThan(2)
    assertThat(string).endsWith("mols")
    assertThat(string).isEmpty()
    assertThat(tomorrow).isAfter(today)
    assertThat(list).contains("a")
    assertThat(list).containsExactly(first, second)
    assertThat(list).hasSize(9)
    assertThat(map).containsKey(2)
    ASSERTJ
    

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92. @MOLSJEROEN
    NESTING MOCKS
    fun `can show alcohol ads when adult`() {
    val userManager = mock(UserManager::class.java)
    val user = mock(User::class.java)
    val userConfig = mock(UserConfiguration::class.java)
    `when`(userManager.getCurrentUser()).thenReturn(user)
    `when`(user.getConfiguration()).thenReturn(userConfig)
    `when`(userConfig.getAge()).thenReturn(21)
    val allowed = Advertisements().alcoholAdsAllowed(userManager)
    assertThat(allowed).isTrue()
    }
    

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93. @MOLSJEROEN
    NESTING MOCKS
    fun `can show alcohol ads when adult`() {
    val userManager = mock(UserManager::class.java)
    val user = mock(User::class.java)
    val userConfig = mock(UserConfiguration::class.java)
    `when`(userManager.getCurrentUser()).thenReturn(user)
    `when`(user.getConfiguration()).thenReturn(userConfig)
    `when`(userConfig.getAge()).thenReturn(21)
    val allowed = Advertisements().alcoholAdsAllowed(userManager)
    assertThat(allowed).isTrue()
    }
    

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94. @MOLSJEROEN
    NESTING MOCKS
    fun `can show alcohol ads when adult`() {
    val user = mock(User::class.java)
    val userConfig = mock(UserConfiguration::class.java)
    `when`(user.getConfiguration()).thenReturn(userConfig)
    `when`(userConfig.getAge()).thenReturn(21)
    val allowed = Advertisements().alcoholAdsAllowed(user)
    assertThat(allowed).isTrue()
    }
    

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95. @MOLSJEROEN
    NESTING MOCKS
    fun `can show alcohol ads when adult`() {
    val user = mock(User::class.java)
    `when`(user.getAge()).thenReturn(21)
    val allowed = Advertisements().alcoholAdsAllowed(user)
    assertThat(allowed).isTrue()
    }
    

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96. @MOLSJEROEN
    PROVIDING TEST DATA
    @Test
    fun `should use mock data`() {
    val mock = mock(UserData::class.java)
    `when`(mock.firstName).thenReturn("FirstName")
    `when`(mock.lastName).thenReturn("LastName")
    `when`(mock.userId).thenReturn(42)
    `when`(mock.street).thenReturn("Street")
    `when`(mock.houseNumber).thenReturn(1)
    `when`(mock.city).thenReturn("City")
    `when`(mock.country).thenReturn("Country")
    // Test code here
    }
    

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97. @MOLSJEROEN
    PROVIDING TEST DATA
    @Test
    fun `should use test data`() {
    val mock = createFakeUserData()
    // Test code here
    }
    fun createFakeUserData() : UserData {
    return UserData("FirstName", "LastName", is 42, "Street", 1, "City", "Country")
    }
    

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98. @MOLSJEROEN
    spy(UserManager::class.java)
    

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99. @MOLSJEROEN
    UNTESTABLE DEPENDENCIES
    Camera
    ViewModel
    

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100. @MOLSJEROEN
     UNTESTABLE DEPENDENCIES
     Camera
     ViewModel CameraWrapper
     

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101. @MOLSJEROEN
     class NativeCamera {
     lateinit var nativeCamera: Camera
     private set
     @Throws(RuntimeException::class)
     fun openNativeCamera() {
     nativeCamera = Camera.open(CameraInfo.CAMERA_FACING_BACK)
     }
     fun releaseNativeCamera() {
     nativeCamera.release()
     }
     }
     UNTESTABLE DEPENDENCIES
     

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102. @MOLSJEROEN
     class NativeCamera {
     lateinit var nativeCamera: Camera
     private set
     @Throws(RuntimeException::class)
     fun openNativeCamera() {
     nativeCamera = Camera.open(CameraInfo.CAMERA_FACING_BACK)
     }
     fun releaseNativeCamera() {
     nativeCamera.release()
     }
     }
     UNTESTABLE DEPENDENCIES
     

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103. @MOLSJEROEN
     WHAT NOT TO UNIT TEST
     UI Layer: Views, Fragments, Activities,…
     Handovers between Threads
     File IO operations
     Database IO operations
     Dependency wrappers
     Deep OS integrations: camera, sensors,…
     ….
     

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104. WRAP UP
     

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105. WE NEED TO BE AS CONFIDENT
     IN THE TESTS WE CODE
     AS WE ARE IN THE CODE WE TEST
     Xavier F. Gouchet
     

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106. @MOLSJEROEN
     TESTS ARE PRODUCTION CODE
     DIFFERENT RULES APPLY (E.G. NO DRY)
     AWESOME TESTS ARE FAST, FOCUSSED AND NON FLAKY
     CODE COVERAGE IS MEANINGLESS
     NOT EVERYTHING NEEDS TO BE TESTED
     

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107. @MOLSJEROEN
     HTTPS://JEROENMOLS.COM/BLOG
     

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108. @MOLSJEROEN
     IMAGE CREDITS
     Welcome image by Clement12

     https://www.flickr.com/photos/clement127/20626915084/in/photolist-Lrdy6N-
     rk5BW3-xqJkdY-Qn7xsS-QS4TQX-RYAGuU-qymdNL-vAg6ro-sa1Wh5-ruMfjM-
     rh9fKo-vTgeEP-qW7Kmv-rVaPtk-rNEdMh-pd8is6-CdNeWN-BkhgMC-xzkZKR-
     rZ6aWZ
     Material design icons by Google

     https://material.io/tools/icons
     Incognito Incognito by Vaibhav Radhakrishnan

     https://thenounproject.com/term/incognito/404950
     

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109. MOLSJEROEN
     

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