Lifecycle-aware class intended to be used to handle periodic tasks. Its main purpose is to handle periodic tasks in a viewmodel (e.g. refreshing a list from a web service)

TickHandler.kt

// Uses packages:
// * org.jetbrains.kotlinx:kotlinx-coroutines-core-jvm:1.6.4

import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Job
import kotlinx.coroutines.delay
import kotlinx.coroutines.isActive
import kotlinx.coroutines.launch
import kotlin.time.Duration

class TickHandler {
    private var job: Job? = null

    fun start(scope: CoroutineScope, interval: Duration, block: suspend () -> Unit) {
        job = scope.launch {
            while (isActive) {
                block()
                delay(interval)
            }
        }
    }

    fun stop() {
        job?.cancel()
    }
}

TickHandlerTest.kt

// Uses packages:
// * org.jetbrains.kotlinx:kotlinx-coroutines-test:1.6.4
// * io.kotest:kotest-runner-junit5:5.5.1
// * io.kotest:kotest-assertions-core:5.5.1
import io.kotest.core.spec.style.FunSpec
import io.kotest.core.test.testCoroutineScheduler
import io.kotest.matchers.shouldBe
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.TestCoroutineScheduler
import kotlin.time.Duration
import kotlin.time.Duration.Companion.milliseconds
import kotlin.time.Duration.Companion.seconds

@OptIn(ExperimentalCoroutinesApi::class, ExperimentalStdlibApi::class)
class TickHandlerTest : FunSpec({
    val tickHandler = TickHandler()

    test("Periodically emits events").config(
        coroutineTestScope = true,
        timeout = 10.seconds
    ) {
        // Arrange
        // An initial delay is added to allow the ticker to immediately emit an event when the
        // ticker is started (probably has to do with initializing the (scope of a) test).
        val initialDelay = 100.milliseconds
        val interval = 1.seconds
        var tickCounter = 0

        // Act
        tickHandler.start(this, interval) { tickCounter++ }
        testCoroutineScheduler.advanceTimeBy(interval * 4 + initialDelay)

        // Assert
        // It should be 5 after 4 seconds, as it immediately emits an event when the ticker is
        // started.
        tickCounter shouldBe 5

        // Tear down
        tickHandler.stop()
    }
})

@OptIn(ExperimentalCoroutinesApi::class)
private fun TestCoroutineScheduler.advanceTimeBy(delay: Duration) =
    advanceTimeBy(delay.inWholeMilliseconds)