Channel vs. Flow

CoroutineTest.kt

package com.example.playground

import com.google.common.truth.Truth.assertThat
import kotlinx.coroutines.channels.ReceiveChannel
import kotlinx.coroutines.channels.produce
import kotlinx.coroutines.channels.toList
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.single
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.yield
import org.junit.Test
import java.util.concurrent.atomic.AtomicBoolean

class CoroutineTest {

    @Test
    fun channel() = runBlocking {
        val called = AtomicBoolean(false)
        assertThat(called.get()).isFalse()
        val c: ReceiveChannel<Int> = produce {
            called.set(true)
            channel.send(1)
        }
        assertThat(called.get()).isFalse()
        yield()
        assertThat(called.get()).isTrue()
        val result = c.toList().single()
        assertThat(called.get()).isTrue()
        assertThat(result).isEqualTo(1)
    }

    @Test
    fun flow() = runBlocking {
        val called = AtomicBoolean(false)
        assertThat(called.get()).isFalse()
        val f = flow {
            called.set(true)
            emit(1)
        }
        assertThat(called.get()).isFalse()
        yield()
        assertThat(called.get()).isFalse()
        val result = f.single()
        assertThat(called.get()).isTrue()
        assertThat(result).isEqualTo(1)
    }
}