KoinAppAlreadyStartedException: A Koin Application has already been started

Question

Using koin-2.0.1 for Android testing and unable to test all 3 test together though each test passes separately.

class NumberFormatterUtilImplTest : KoinTest {

    private val numberFormatterUtil: NumberFormatterUtilImpl by inject()

    @Before
    fun setUp() {
        startKoin { modules(utilsModule) }
    }

    @Test
    fun `does formatter returns two digit faction if supplied one digit value`() {
        val result = numberFormatterUtil.getAdjustedCurrencyRate(18.0)
        Assert.assertEquals(result, 18.00, 1.0)
    }

    @Test
    fun `does formatter returns two digit faction if supplied multiple digits value`() {
        val result = numberFormatterUtil.getAdjustedCurrencyRate(18.12343)
        Assert.assertEquals(result, 18.12, 1.0)
    }

    @Test
    fun `does formatter returns rounded two digit faction if supplied multiple digits value`() {
        val result = numberFormatterUtil.getAdjustedCurrencyRate(18.12876)
        Assert.assertEquals(result, 18.13, 1.0)
    }
}

running class level testing resulting below:

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

any input would be helpful, thanks.

Answer 1

A common practice is to pair @Before setup with @After cleanup. You can call stopKoin() there so the next call to startKoin() works again:

@After
fun tearDown() {
    stopKoin()
}

Answer 2

Call stopKoin() on @Before and @After method like below:

import com.my.example.appModule
import android.os.Build
import androidx.test.core.app.ApplicationProvider
import org.junit.Before
import org.junit.Test
import org.junit.runner.RunWith
import org.koin.android.ext.koin.androidContext
import org.koin.core.context.startKoin
import org.koin.core.context.stopKoin
import org.koin.test.KoinTest
import org.koin.test.inject
import org.robolectric.RobolectricTestRunner
import org.robolectric.annotation.Config
import java.util.*

@Config(sdk = [Build.VERSION_CODES.LOLLIPOP])
@RunWith(RobolectricTestRunner::class)
class SomeRepositoryTest: KoinTest {

    // Return Completable of RxJava
    private val repository: SomeRepository by inject()

    @Before
    fun before() {
        stopKoin() // to remove 'A Koin Application has already been started'
        startKoin {
            androidContext(ApplicationProvider.getApplicationContext())
            modules(appModule)
        }
    }

    @After
    fun after() {
        stopKoin()
    }

    @Test
    fun testSomething() {

        repository.insert("data").blockingAwait()

        assert(true)
    }
}

Answer 3

As an alternative to the @After approach, you can also use AutoCloseKoinTest. As described in the docs:

Extended Koin Test - embed autoclose @after method to close Koin after every test

Instead of extending KoinTest, you can extend AutoCloseKoinTest and it will do the after test for you.