Turbine

Learn Flow testing with Turbine.

Testing Flows with Turbine

Turbine is a library for testing Kotlin Flows. With flow.test { } you subscribe to the flow and use awaitItem and awaitComplete to wait for the next item and completion.

Example: val flow = flowOf(1, 2, 3); flow.test { assertEquals(1, awaitItem()); assertEquals(2, awaitItem()); awaitComplete() }. Turbine makes it easy to check items in order; it removes timing flakiness.

awaitItem and awaitComplete

awaitItem returns the next item emitted by the flow. awaitComplete verifies that the flow has completed. These two methods are the core of step-by-step flow testing.

Example: flow.test { val first = awaitItem(); val second = awaitItem(); awaitComplete() }. Each call to awaitItem gives the next item. If the order is wrong, the test fails. This guarantees items are emitted in the expected order.

Exercise Test a Flow with Turbine

Define a function scoreFlow that returns flowOf(10, 20, 30). In main open a scoreFlow().test { } block and print each awaitItem() result with println.

Show example solution

import kotlinx.coroutines.flow.flowOf
import kotlinx.coroutines.flow.Flow
import app.cash.turbine.test

fun scoreFlow(): Flow<Int> = flowOf(10, 20, 30)

fun main() = scoreFlow().test {
    println(awaitItem())
    println(awaitItem())
    println(awaitItem())
}

Test yourself

Complete the .test block

val flow = flowOf(1, 2, 3)
flow.____ {
    assertEquals(1, awaitItem())
    awaitComplete()
}

Show answer

val flow = flowOf(1, 2, 3)
flow.test {
    assertEquals(1, awaitItem())
    awaitComplete()
}

When testing a Flow with Turbine, which method returns the next emitted item?
- collect
- next
- awaitItem
- fetch
Show answer

awaitItem — awaitItem returns the next item emitted by the flow.
Match the Turbine methods

flow.test { }

Start subscription
awaitItem()

Next item
awaitComplete()

Completion
expectNoEvents()

No events

Next lesson: Advanced MockK

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