KotlinTest with Koin: InvocationTargetException - unit-testing

Question

I'm unable to use Koin 2.0.1 with Kotlin-test 3.4.2. I get an InvocationTargetException like this:
Running koinexample.KoinSampleTests
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.009 sec <<< FAILURE! - in koinexample.KoinSampleTests
koinexample.KoinSampleTests Time elapsed: 0.009 sec <<< ERROR!
java.lang.reflect.InvocationTargetException
at koinexample.KoinSampleTests.getKoin(KoinSampleTests.kt:26)
at koinexample.KoinSampleTests.<init>(KoinSampleTests.kt:61)
I've created a small example on GitHub that reproduces this error:
https://github.com/elifarley/kotlin-tests-with-koin-examples
Just execute these commands to clone the repo and run tests:
git clone https://github.com/elifarley/kotlin-tests-with-koin-examples.git
cd kotlin-tests-with-koin-examples
mvn
Here's the main Kotlin file:
package koinexample
import io.kotlintest.koin.KoinListener
import io.kotlintest.shouldBe
import io.kotlintest.specs.FreeSpec
import org.koin.core.inject
import org.koin.dsl.module
import org.koin.test.KoinTest
data class Stats(var ok: Long = 0, var error: Long = 0)
interface StatsServer {
fun newError(): Long
}
class StatsServerSimple(private val stats: Stats) : StatsServer {
override fun newError() = stats.error++
}
val appModule = module {
single { Stats() }
single { StatsServerSimple(get()) as StatsServer }
}
class KoinSampleTests : FreeSpec(), KoinTest {
private val modules = listOf(
appModule
)
override fun listeners() = listOf(KoinListener(modules))
val statsServer: StatsServer by inject()
init {
"Happy path" {
statsServer.newError() shouldBe 1
}
}
}

Answer 1

Your issue seems to be a simple import confusion.
Note that you're using import org.koin.core.inject, which is this function:
inline fun <reified T> KoinComponent.inject(
qualifier: Qualifier? = null,
noinline parameters: ParametersDefinition? = null
): Lazy<T> =
getKoin().inject(qualifier, parameters)
It needs getKoin to work, and therefore you cannot initialize your test (The test class is initialized before Koin had a chance to start with the listener).
The correct import is import org.koin.test.inject, which translates to:
inline fun <reified T> KoinTest.inject(
qualifier: Qualifier? = null,
noinline parameters: ParametersDefinition? = null
): Lazy<T> = lazy { get<T>(qualifier, parameters) }
Take note that this is indeed lazy, so Kotest will have a chance to initialize Koin before your tests start.
Fixing that import should resolve this issue

Answer 2

Seems like you're never starting the Koin app. You need to have
startKoin {
modules(appModule)
}
in your test method or in the beforeSpec/beforeTest function call of the spec.
Or use something like here:
override fun listeners() = listOf(KoinListener(appModule))
which is described in the documentation for kotlintest/kotest: https://github.com/Kotest/Kotest/blob/master/doc/extensions.md#koin