Write awesome unit tests

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@MOLSJEROEN WRITE AWESOME UNIT TESTS

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@MOLSJEROEN @MOLSJEROEN

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

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CORE PRINCIPLES

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@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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WE WRITE TESTS TO RUN THEM

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@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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TESTS ARE PRODUCTION C0DE

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@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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OPTIMIZE TESTS FOR FAILURE

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THREE GROUND RULES

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@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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@MOLSJEROEN

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

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@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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@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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@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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CODE COVERAGE

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

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

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

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

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@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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@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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@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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@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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@MOLSJEROEN Coverage Effort

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@MOLSJEROEN

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TEST DRIVEN DEVELOPMENT

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@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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@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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@MOLSJEROEN Green Red Refactor

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

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@MOLSJEROEN class CalculatorTest { }

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

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

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@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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@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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@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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@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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@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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TESTING MYTHS

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TESTING SLOWS DOWN DEVELOPMENT

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TESTING IS HARD

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TEST CODE IS NOT PRODUCTION CODE

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SIMPLE CODE SHOULDN’T BE TESTED

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TESTING NEGATIVELY IMPACTS THE PRODUCTION CODE

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EVERYTHING SHOULD BE TESTED

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TEST VS PRODUCTION CODE

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

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USE JUNIT 4 SYNTAX

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

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

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

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KEEP READER IN TEST

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@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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@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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@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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NO CLUTTER

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

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

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OPTIMIZE TEST FOR FAILURE

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

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TIPS

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@MOLSJEROEN TESTING UI View ViewModel Repository LiveData

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

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

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@MOLSJEROEN UNTESTABLE DEPENDENCIES Camera ViewModel

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@MOLSJEROEN UNTESTABLE DEPENDENCIES Camera ViewModel CameraWrapper

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@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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@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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WRAP UP

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

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@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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MOLSJEROEN