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Exercise: Flow testing

Test the observeAppointments function from the ObserveAppointmentsUseCase class. Starting code:

class ObserveAppointmentsUseCase(
    private val appointmentRepository: AppointmentRepository
) {
    fun observeAppointments(): Flow<List<Appointment>> =
        appointmentRepository
        .observeAppointments()
        .filterIsInstance<AppointmentUpdate>()
        .map { it.appointments }
        .distinctUntilChanged()
        .retry { it is ApiException && it.code in 500..599 }
}

interface AppointmentRepository {
    fun observeAppointments(): Flow<AppointmentEvent>
}

sealed class AppointmentEvent
data class AppointmentUpdate(
    val appointments: List<Appointment>
) : AppointmentEvent()
data object AppointmentConfirmed : AppointmentEvent()
data class Appointment(val title: String, val time: Instant)
data class ApiException(val code: Int) : Throwable()

You should test the following cases:

  • should receive only appointment lists from appointment updates
  • should not receive non-distinct values
  • should retry exceptions of type ApiException with code 5XX

This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in coroutines/flow/ObserveAppointmentsUseCase.kt. You can find there starting code.

Playground

import kotlinx.coroutines.flow.*
import java.time.Instant

class ObserveAppointmentsUseCase(
    private val appointmentRepository: AppointmentRepository
) {
    fun observeAppointments(): Flow<List<Appointment>> =
        appointmentRepository
        .observeAppointments()
        .filterIsInstance<AppointmentUpdate>()
        .map { it.appointments }
        .distinctUntilChanged()
        .retry { it is ApiException && it.code in 500..599 }
}

interface AppointmentRepository {
    fun observeAppointments(): Flow<AppointmentEvent>
}

sealed class AppointmentEvent
data class AppointmentUpdate(
    val appointments: List<Appointment>
) : AppointmentEvent()
data object AppointmentConfirmed : AppointmentEvent()
data class Appointment(val title: String, val time: Instant)
data class ApiException(val code: Int) : Throwable()