Q:

KotlinTest with Koin: InvocationTargetException

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
        }
    }
}

A:

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

