Testing Ktor application fails with "A Koin Application has already been started"

I am trying to unit test a ktor application powered by koin, described as follows:

• The gradle.properties:

ktor_version=1.2.2
kotlin_version=1.3.40
logback_version=1.2.1

• The build.gradle’s dependencies:

dependencies {
    compile("org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version")
    compile("io.ktor:ktor-server-netty:$ktor_version")
    compile("ch.qos.logback:logback-classic:$logback_version")
    compile("org.koin:koin-ktor:2.0.1")
    testCompile("io.ktor:ktor-server-tests:$ktor_version")
    testCompile("org.koin:koin-test:0.9.3")
}

• The resources/application.conf:

ktor {
    deployment {
        port = 8080
    }
    application {
        modules = [com.example.MainApplicationKt.main]
    }
}

• The com.example.MainApplication.kt:

package com.example

// imports...

interface HelloController {
    suspend fun onGetHello(call: ApplicationCall)
}

class DefaultHelloController() : HelloController {
    override suspend fun onGetHello(call: ApplicationCall) {
        call.respondText("Hello World!")
    }
}

fun main(args: Array<String>) {
    embeddedServer(Netty, commandLineEnvironment(args)).start()
}

fun Application.main() {
    install(DefaultHeaders)
    install(CallLogging)
    install(org.koin.ktor.ext.Koin) {
        modules(helloModule)
    }
    val helloController: HelloController by inject()
    routing {
        get("/hello") {
            helloController.onGetHello(call)
        }
    }
}

• and finally the MainApplicationTest.kt:

class MainApplicationTest {

    private object MockHelloController : HelloController {
        override suspend fun onGetHello(call: ApplicationCall) {
            call.respondText("Mocked Hello World!")
        }
    }

    @Before
    fun setup() {
        val mockHelloModule = module {
            single<HelloController> { MockHelloController }
        }
        startKoin {
            listOf(mockHelloModule)
        }
    }

    @After
    fun teardown() {
        stopKoin()
    }

    @Test
    fun testRequestsOK() = withTestApplication(Application::main) {
        with(handleRequest(HttpMethod.Get, "/hello")) {
            assertEquals(HttpStatusCode.OK, response.status())
            assertEquals("Mocked Hello World!", response.content)
        }
    }
}

When running the unit test, I get the following exception:

org.koin.core.error.KoinAppAlreadyStartedException: A Koin Application has already been started

What is the proper way to setup my unit tests?

Thanks in advance, Regards, Romain

[iRYO400]

Oops, that was easier than I thought. Just add stopKoin() inside

    @After
    fun tearDown() {
        stopKoin()
    }

[bio007]

I’m facing similar problem with robolectric. See this issue https://github.com/robolectric/robolectric/issues/3108

I think it’s a problem Koin is having some static variables remembering previous runs (tests). This way the tests are not isolated and something can go wrong…