async function test with Kotlin, junit and Truth

SampleAsyncTest.kt

import com.google.common.truth.Truth.assertThat // https://truth.dev/
import junit.framework.TestCase
import kotlinx.coroutines.*
import org.junit.Test

class SampleAsyncTest : TestCase() {

    suspend fun sampleFunctionToTest(): String {
        delay(1000)
        return "failure"
    }

    @Test
    fun testAsync() {
        var failureMessage: String? = ""
        // Exception in coroutine cannot be catched by general try-catch
        // So define CoroutineExceptionHandler
        // https://kotlinlang.org/docs/exception-handling.html#cancellation-and-exceptions
        val coroutineExceptionHandler = CoroutineExceptionHandler { _, exception ->
            failureMessage = exception.message
        }
        runBlocking { // wait testing function complete
            GlobalScope.launch(coroutineExceptionHandler) {
                // Call async function to Test
                val sampleVal = async { sampleFunctionToTest() }
                // assertThat the value as normal
                // If it fails, it causes exception in coroutine
                assertThat(sampleVal.await()).isEqualTo("success")
            }.join()
        }
        // Check if there was no exception
        assertThat(failureMessage).isEmpty()
    }
}