Migrating Junit4 tests to androidx: What causes 'delegate runner could not be loaded'?

Question

I am migrating my app to androidx, I can\'t seem to get my unit tests working. I took example from Google\'s AndroidJunitRunnerSample, which has been updated to use the new

Answer 1

Some other possible reasons:

• Having only @SmallTest (or Medium-/Large-) test methods. Marking at least one method with @Test solves the issues.
• setup() / teardown() methods are not public.

Answer 2

If after adding the following dependencies:

testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 
           'com.android.support.test.espresso:espresso-core:3.0.1'

and

android{
defaultConfig{
    ...
    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    ...
   }
}

doesn't help then use the deprecated AndroidJUnit4 class which belongs to the androidx.test.runner package instead of the one belongs to androidx.test.ext.junit.runners.AndroidJUnit4 package.

I still don't understand why AndroidJUnit4 class is deprecated while the Gradle dependencies it belongs to is suggested by the Android team everywhere i.e Codelabs and docs

Answer 3

You also get the error message if you use a test rule in Kotlin and write it Java style

@Rule
var mainActivityActivityTestRule = ActivityTestRule(MainActivity::class.java)

You have to change @Rule to @get:Rule

@get:Rule
var mainActivityActivityTestRule = ActivityTestRule(MainActivity::class.java) 

Answer 4

Removing @RunWith(AndroidJUnit4.class) annotations from the test classes fixed the issue, although I can't really say why or how it fixed it.

Edit: Allright I did some more testing. I migrated my app to Kotlin, and suddenly I noticed the tests began to work with the @RunWith annotation, too. Here's what I found out:

import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;

import androidx.test.ext.junit.runners.AndroidJUnit4;

@RunWith(AndroidJUnit4.class) // <-- @RunWith + @BeforeClass = Error
public class AndroidXJunitTestJava {

    @BeforeClass
    public static void setup() {
        // Setting up once before all tests
    }

    @Test
    public void testing() {
        // Testing....
    }
}

This java test fails with the Delegate runner for AndroidJunit4 could not be loaded error. But If I remove the @RunWith annotation, it works. Also, if I replace the @BeforeClass setup with just a @Before, like this:

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;

import androidx.test.ext.junit.runners.AndroidJUnit4;

@RunWith(AndroidJUnit4.class) // <-- @RunWith + @Before = works?
public class AndroidXJunitTestJava {

    @Before
    public void setup() {
        // Setting up before every test
    }

    @Test
    public void testing() {
        // Testing....
    }
}

The tests will run without errors. I needed to use the @BeforeClass annotation, so I just removed @RunWith.

But now that I am using Kotlin, the following (which should be equal to the first java example) works:

import androidx.test.ext.junit.runners.AndroidJUnit4
import org.junit.BeforeClass
import org.junit.Test
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class AndroidXJunitTest {

    companion object {
        @BeforeClass fun setup() {
            // Setting up
        }
    }

    @Test
    fun testing() {
        // Testing...
    }

}

Also, as Alessandro Biessek said in an answer and @Ioane Sharvadze in the comments, the same error can happen with the @Rule annotation. If I add a line

 @Rule val instantTaskExecutorRule = InstantTaskExecutorRule()

To the Kotlin example, the same delegate runner error happens. This must be replaced with

@get:Rule val instantTaskExecutorRule = InstantTaskExecutorRule()

Explanation here.

Answer 5

I fixed with this configuration:

My dependencies:

/*Instrumentation Test*/
androidTestImplementation "org.assertj:assertj-core:3.12.2"
androidTestImplementation ('androidx.test.espresso:espresso-core:3.2.0',{
    exclude group: 'com.android.support', module: 'support-annotations'
})
androidTestImplementation "androidx.arch.core:core-testing:2.1.0-rc01"

In my defaultConfig section I have:

defaultConfig {
    applicationId "uy.edu.ude.archcomponents"
    minSdkVersion 22
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

    testInstrumentationRunnerArguments clearPackageData: 'true'
}

In the test I have:

package uy.edu.ude.archcomponents.repository

import androidx.arch.core.executor.testing.InstantTaskExecutorRule
import androidx.room.Room
import androidx.test.platform.app.InstrumentationRegistry
import androidx.test.runner.AndroidJUnit4
import com.example.android.roomwordssample.WordDao
import com.example.android.roomwordssample.WordRoomDatabase
import kotlinx.coroutines.runBlocking
import org.assertj.core.api.Assertions.assertThat
import org.junit.After
import org.junit.Before
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import uy.edu.ude.archcomponents.entity.Word
import java.io.IOException


@RunWith(AndroidJUnit4::class)
class WordDaoTest {

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    private lateinit var wordDao: WordDao
    private lateinit var db: WordRoomDatabase

    @Before
    fun createDb() {
        val context = InstrumentationRegistry.getInstrumentation().context
        // Using an in-memory database because the information stored here disappears when the
        // process is killed.
        db = Room.inMemoryDatabaseBuilder(context, WordRoomDatabase::class.java)
                // Allowing main thread queries, just for testing.
                .allowMainThreadQueries()
                .build()
        wordDao = db.wordDao()
    }

    @After
    @Throws(IOException::class)
    fun closeDb() {
        db.close()
    }

    @Test
    @Throws(Exception::class)
    fun insertAndGetWord() {
        runBlocking {
            val word = Word("word")
            wordDao.insert(word)
            val allWords = wordDao.getAlphabetizedWords().waitForValue()
            assertThat(allWords[0].word).isEqualTo(word.word)
        }
    }
}

I also use the android plugin version 3.4.2. I took the config from here

Answer 6

For me the problem was the @Rule annotation..
I don't know the cause for now.

As a temporary workaround yo can for example start your activity using UIAutomator for ActivityTestRule.