Kotlin - Don't run unit test until lateinit property is initialized - kotlin

Question

I have a case where the unit of code I'm testing is running on a different thread and so the test executes and fails before the unit has finished executing:
class Tests {
private lateinit var result: String
#BeforeAll
fun setup() {
DataService().subscribe {
result = it
}
}
#Test
fun `get result from data service`() {
assert(result.contains("Hello"))
}
}
When the test runs, I get the following exception:
kotlin.UninitializedPropertyAccessException: lateinit property result has not been initialized
How can I ensure that the tests don't run before result has been initialized?

Answer 1

The test in the provided form won't work: #BeforeAll is allowed only on static methods, but then it couldn't access the result field. It can be solved by using #BeforeEach and #TestInstance(TestInstance.Lifecycle.PER_METHOD) [but see the UPDATE at the end of the post]
Regarding the result initialization itself: you can check if it has been initialized using this::result.isInitialized, e.g.:
#TestInstance(TestInstance.Lifecycle.PER_METHOD)
class AwaitTest {
private lateinit var result: String
#BeforeEach
fun setup() {
DataService().subscribe {
result = it
}
}
#Test
fun `get result from data service`() = runBlocking {
awaitInitialization()
assert(result.contains("Hello"))
}
suspend fun awaitInitialization() {
while(!this::result.isInitialized) {
delay(100)
}
}
}
Alternatively you could use awaitility:
#TestInstance(TestInstance.Lifecycle.PER_METHOD)
class AwaitTest {
private lateinit var result: String
#BeforeEach
fun setup() {
DataService().subscribe {
result = it
}
}
#Test
fun `get result from data service`() {
await until { this#AwaitTest::result.isInitialized }
assert(result.contains("Hello"))
}
}
Or even better, move await to the setup() method:
#TestInstance(TestInstance.Lifecycle.PER_METHOD)
class AwaitTest {
private lateinit var result: String
#BeforeEach
fun setup() {
DataService().subscribe {
result = it
}
await until { this#AwaitTest::result.isInitialized }
}
#Test
fun `get result from data service`() {
assert(result.contains("Hello"))
}
}
UPDATE:
Actually a #BeforeAll method doesn't need to be static if the test class is annotated with the#TestInstance(TestInstance.Lifecycle.PER_CLASS):
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
class AwaitTest {
private lateinit var result: String
#BeforeAll
fun setup() {
DataService().subscribe {
result = it
}
await until { this#AwaitTest::result.isInitialized }
}
#Test
fun `get result from data service`() {
assert(result.contains("Hello"))
}
}