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Ragunath Jawahar • @ragunathjawahar • https://ragunath.xyz Building Robust Software Episode 3: Not going to convince you to write tests

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Episode 1: Small ideas, big impact • Robustness principle & a tweaked version of it • Algebraic data types • Total & partial functions • Minimising defensive programming • Using the type system to short-circuit failures (a.k.a failing fast) • Avoiding primitive obsession

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Episode 2: Exceptions, side-effects and boundaries • Exception anti-patterns • Handling • Throwing • Tester-Doer pattern • Try-Parse Pattern • Converting exceptions to values • Introduction to values as boundaries • Architectures that use values as boundaries

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Building Robust Software Playlist https://bit.ly/3F2ijgm

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< / recap>

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Why this talk?

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Scenario An event management startup has hired you and needs your help to build a feature that sends reminder emails to potential attendees for an upcoming event.

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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Scenario Your company is losing money 💸 💸 💸 due to bug fi xes in production, so your team has decided to write tests. It's your responsibility to bring your modules under test.

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🤔

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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Test: No registrations

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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@Test fun `don't send emails when there are no registrants`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) whenever(dao.getRegistrants(event.id)).thenReturn(emptyList()) val event = Event( "Building Robust Software III", "Event is on 16th December, please attend." ) // when eventManager.sendReminder(event) // then verifyNoInteractions(mailer) }

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Test: A mix of “Yes”, “No” and “Maybe”

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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@Test fun `email only those who RSVP'd yes and maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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✅ No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” ✅ A mix of “Yes”, “No” and “Maybe”

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Behaviour testing

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Event Manager Event Dao Mailer

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Event Manager Event Dao Mailer System under test (SUT)

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Event Manager Event Dao Mailer Collaborators

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Collaborators • Real thing • Sorta real thing

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Sorta real thing • Stubs • Mocks • Fakes • Dummies • Spies https://martinfowler.com/articles/mocksArentStubs.html

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Current EventManager design • Encapsulates business logic • Who should be noti fi ed?

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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Current EventManager design • Encapsulates business logic • Who should be noti fi ed? • Coordination logic • Who is talking to who?

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES || it.rsvp = = MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } a.EventManager.kt

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Current EventManager design • Encapsulates business logic • Who should be noti fi ed? • Coordination logic • Who is talking to who?

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Testing the business logic

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Testing the business logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Testing the business logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Testing the business logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Testing the business logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Testing the business logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Testing the coordination logic

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Testing the coordination logic verifyNoInteractions(mailer) verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer)

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Do-Over

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .potentialAttendees() potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES | | it.rsvp == MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } }

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .potentialAttendees() potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES | | it.rsvp == MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } }

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class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .potentialAttendees() potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } } class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .filter { it.rsvp == YES | | it.rsvp == MAYBE } potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } }

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b.EventManager.kt class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .potentialAttendees() potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } }

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b.EventManager.kt class EventManager( private val dao: EventDao, private val mailer: Mailer ) { fun sendReminder(event: Event) { val registrants = dao.getRegistrants(event.id) val potentialAttendees = registrants .potentialAttendees() potentialAttendees.onEach { attendee -> mailer.mail(attendee.emailAddress, event.reminder) } } }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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Users.kt fun List.potentialAttendees(): List = this.filter { user -> user.rsvp = = Rsvp.YES | | user.rsvp == Rsvp.MAYBE }

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No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” A mix of “Yes”, “No”, and “Maybe”

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Test: No registrations

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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@Test fun `no potential attendees for an empty list`() { // given val noRegistrants = emptyList() // when val potentialAttendees = noRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .isEmpty() }

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Test: A mix of “Yes”, “No” and “Maybe”

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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@Test fun `potential attendees contains only registrants those who RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) }

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✅ No registrations Everyone RSVP’d “Yes” Everyone RSVP’d “No” Everyone RSVP’d “Maybe” ✅ A mix of “Yes”, “No” and “Maybe”

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🤨

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Value testing

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I O

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I O Input

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I O Output

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I O System under test (SUT)

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Collaborators • None • We use real things

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Newer EventManager design • Does not encapsulate business logic • Can use micro unit tests to test various cases • Value-in, value-out results in decoupled design • No dependencies for business logic

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Testing the business logic assertThat(potentialAttendees) .isEmpty() assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) )

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Testing the business logic assertThat(potentialAttendees) .isEmpty() assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) )

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Testing the business logic assertThat(potentialAttendees) .isEmpty() assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) )

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Testing the business logic assertThat(potentialAttendees) .isEmpty() assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) )

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Testing the business logic assertThat(potentialAttendees) .isEmpty() assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) )

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Testing the coordination logic @Test fun `query and email folks who RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Implementation A vs. B @Test fun `RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) } @Test fun `RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Implementation A vs. B @Test fun `RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) } @Test fun `RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Implementation A vs. B @Test fun `RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) } @Test fun `RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Implementation A vs. B @Test fun `RSVP'd yes or maybe`() { // given val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) // when val potentialAttendees = allRegistrants.potentialAttendees() // then assertThat(potentialAttendees) .containsExactly( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.MAYBE) ) } @Test fun `RSVP'd yes and maybe to the event`() { // given val dao = mock() val mailer = mock() val eventManager = EventManager(dao, mailer) val event = Event( 1, "Building Robust Software III", "Event is on 16th December, please attend." ) val allRegistrants = listOf( User("[email protected]", Rsvp.YES), User("[email protected]", Rsvp.NO), User("[email protected]", Rsvp.MAYBE) ) whenever(dao.getRegistrants(event.id)).thenReturn(allRegistrants) // when eventManager.sendReminder(event) // then verify(mailer).mail("[email protected]", event.reminder) verify(mailer).mail("[email protected]", event.reminder) verifyNoMoreInteractions(mailer) }

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B import com.google.common.truth.Truth.assertThat import org.junit.jupiter.api.Test import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User import org.junit.jupiter.api.Test import org.mockito.kotlin.mock import org.mockito.kotlin.verify import org.mockito.kotlin.verifyNoInteractions import org.mockito.kotlin.verifyNoMoreInteractions import org.mockito.kotlin.whenever import xyz.ragunath.events.Event import xyz.ragunath.events.EventDao import xyz.ragunath.events.Mailer import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User

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Implementation A vs. B import com.google.common.truth.Truth.assertThat import org.junit.jupiter.api.Test import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User import org.junit.jupiter.api.Test import org.mockito.kotlin.mock import org.mockito.kotlin.verify import org.mockito.kotlin.verifyNoInteractions import org.mockito.kotlin.verifyNoMoreInteractions import org.mockito.kotlin.whenever import xyz.ragunath.events.Event import xyz.ragunath.events.EventDao import xyz.ragunath.events.Mailer import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User

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Implementation A vs. B import com.google.common.truth.Truth.assertThat import org.junit.jupiter.api.Test import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User import org.junit.jupiter.api.Test import org.mockito.kotlin.mock import org.mockito.kotlin.verify import org.mockito.kotlin.verifyNoInteractions import org.mockito.kotlin.verifyNoMoreInteractions import org.mockito.kotlin.whenever import xyz.ragunath.events.Event import xyz.ragunath.events.EventDao import xyz.ragunath.events.Mailer import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User

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Implementation A vs. B import com.google.common.truth.Truth.assertThat import org.junit.jupiter.api.Test import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User import org.junit.jupiter.api.Test import org.mockito.kotlin.mock import org.mockito.kotlin.verify import org.mockito.kotlin.verifyNoInteractions import org.mockito.kotlin.verifyNoMoreInteractions import org.mockito.kotlin.whenever import xyz.ragunath.events.Event import xyz.ragunath.events.EventDao import xyz.ragunath.events.Mailer import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B import com.google.common.truth.Truth.assertThat import org.junit.jupiter.api.Test import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User import org.junit.jupiter.api.Test import org.mockito.kotlin.mock import org.mockito.kotlin.verify import org.mockito.kotlin.verifyNoInteractions import org.mockito.kotlin.verifyNoMoreInteractions import org.mockito.kotlin.whenever import xyz.ragunath.events.Event import xyz.ragunath.events.EventDao import xyz.ragunath.events.Mailer import xyz.ragunath.events.Rsvp import xyz.ragunath.events.User

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Implementation A vs. B • 5 integration tests • + Dependencies • ↑ Coupling • Wider change propagation • Harder to maintain • More assertions • 5 micro-unit tests • 1 integration test • - Dependencies • ↓ Coupling • Limited change propagation • Easier to maintain • Fewer assertions 💯

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Destroy All Software—Boundaries https://bit.ly/3yuuxvQ

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What did we learn? • Behaviour testing • Value testing • Micro-unit tests • Complementary tests • Integration tests

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Scenario You inherit a codebase that does not have any tests, the previous developers have left the organisation and you are expected to enhance an existing feature.

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package com.gildedrose class GildedRose(var items: Array) { fun updateQuality() { for (i in items.indices) { if (items[i].name != "Aged Brie" && items[i].name ! = "Backstage passes to a TAFKAL80ETC concert") { if (items[i].quality > 0) { if (items[i].name != "Sulfuras, Hand of Ragnaros") { items[i].quality = items[i].quality - 1 } } } else { if (items[i].quality < 50) { items[i].quality = items[i].quality + 1 if (items[i].name == "Backstage passes to a TAFKAL80ETC concert") { if (items[i].sellIn < 11) { if (items[i].quality < 50) { items[i].quality = items[i].quality + 1 } } if (items[i].sellIn < 6) { if (items[i].quality < 50) { items[i].quality = items[i].quality + 1 } } } } } if (items[i].name != "Sulfuras, Hand of Ragnaros") { items[i].sellIn = items[i].sellIn - 1 } if (items[i].sellIn < 0) { if (items[i].name != "Aged Brie") { if (items[i].name != "Backstage passes to a TAFKAL80ETC concert") { if (items[i].quality > 0) { if (items[i].name != "Sulfuras, Hand of Ragnaros") { items[i].quality = items[i].quality - 1 } } } else { items[i].quality = items[i].quality - items[i].quality } } else { if (items[i].quality < 50) { items[i].quality = items[i].quality + 1 } } } } } }

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Writing tests for code you wrote vs. Writing tests for someone else’s code (characterisation tests)

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@Test fun `aged brie`() { // given val itemName = "Aged Brie" val sellIns = arrayOf(-1, 0, 1, 5, 6, 7, 10, 11, 12) val qualities = arrayOf(-1, 0, 1, 49, 50, 51) // when val function = updateQualityFunction(itemName) // (Int, Int) - > String // then CombinationApprovals.verifyAllCombinations(function, sellIns, qualities) }

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@Test fun `aged brie`() { // given val itemName = "Aged Brie" val sellIns = arrayOf(-1, 0, 1, 5, 6, 7, 10, 11, 12) val qualities = arrayOf(-1, 0, 1, 49, 50, 51) // when val function = updateQualityFunction(itemName) // (Int, Int) - > String // then CombinationApprovals.verifyAllCombinations(function, sellIns, qualities) }

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@Test fun `aged brie`() { // given val itemName = "Aged Brie" val sellIns = arrayOf(-1, 0, 1, 5, 6, 7, 10, 11, 12) val qualities = arrayOf(-1, 0, 1, 49, 50, 51) // when val function = updateQualityFunction(itemName) // (Int, Int) - > String // then CombinationApprovals.verifyAllCombinations(function, sellIns, qualities) }

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[-1, -1] => [Aged Brie, -2, 1] [-1, 0] => [Aged Brie, -2, 2] [-1, 1] => [Aged Brie, -2, 3] [-1, 49] => [Aged Brie, -2, 50] [-1, 50] => [Aged Brie, -2, 50] [-1, 51] => [Aged Brie, -2, 51] [0, -1] => [Aged Brie, -1, 1] [0, 0] => [Aged Brie, -1, 2] [0, 1] => [Aged Brie, -1, 3] [0, 49] => [Aged Brie, -1, 50] [0, 50] => [Aged Brie, -1, 50] [0, 51] => [Aged Brie, -1, 51] [1, -1] => [Aged Brie, 0, 0] [1, 0] => [Aged Brie, 0, 1] [1, 1] => [Aged Brie, 0, 2] [1, 49] => [Aged Brie, 0, 50] [1, 50] => [Aged Brie, 0, 50] [1, 51] => [Aged Brie, 0, 51] [5, -1] => [Aged Brie, 4, 0] [5, 0] => [Aged Brie, 4, 1] [5, 1] => [Aged Brie, 4, 2] [5, 49] => [Aged Brie, 4, 50] [5, 50] => [Aged Brie, 4, 50] [5, 51] => [Aged Brie, 4, 51] [6, -1] => [Aged Brie, 5, 0] [6, 0] => [Aged Brie, 5, 1] [6, 1] => [Aged Brie, 5, 2] [6, 49] => [Aged Brie, 5, 50] [6, 50] => [Aged Brie, 5, 50] [6, 51] => [Aged Brie, 5, 51] [7, -1] => [Aged Brie, 6, 0] [7, 0] => [Aged Brie, 6, 1] [7, 1] => [Aged Brie, 6, 2] [7, 49] => [Aged Brie, 6, 50] [7, 50] => [Aged Brie, 6, 50] [7, 51] => [Aged Brie, 6, 51] [10, -1] => [Aged Brie, 9, 0] [10, 0] => [Aged Brie, 9, 1] [10, 1] => [Aged Brie, 9, 2] [10, 49] => [Aged Brie, 9, 50] [10, 50] => [Aged Brie, 9, 50] [10, 51] => [Aged Brie, 9, 51] [11, -1] => [Aged Brie, 10, 0] [11, 0] => [Aged Brie, 10, 1] [11, 1] => [Aged Brie, 10, 2] [11, 49] => [Aged Brie, 10, 50] [11, 50] => [Aged Brie, 10, 50] [11, 51] => [Aged Brie, 10, 51] [12, -1] => [Aged Brie, 11, 0] [12, 0] => [Aged Brie, 11, 1] [12, 1] => [Aged Brie, 11, 2] [12, 49] => [Aged Brie, 11, 50] [12, 50] => [Aged Brie, 11, 50] [12, 51] => [Aged Brie, 11, 51]

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Refactor ✌

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Approval Tests • Snapshot testing, golden master testing, etc., • Helps bring large portions of code under tests quickly • Can work on di ff erent kinds of data

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Approval Tests • https://github.com/approvals/ApprovalTests.Java • https://github.com/approvals/ApprovalTests.Plugins.IntelliJ • https://github.com/approvals

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More testing tools & techniques • Performance testing • Property testing

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Workflows • TDD • https://www.coderetreat.org/ • TCR • https://medium.com/@kentbeck_7670/test-commit-revert-870bbd756864 • https://github.com/LarsEckart/tcr-extension • https://github.com/ragunathjawahar/GildedRose-Refactoring-Kata/tree/rj/ attempt-04

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Fin Questions? @ragunathjawahar • https://ragunath.xyz