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java.lang.RuntimeException: Delegate runner androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner for AndroidJUnit4 could not be found

I am new to android testing and I don´t know how to solve this problem.
Trying to run the following test file from my project:
#RunWith(AndroidJUnit4::class)
class AppDatabaseTest {
private lateinit var userDAO: UserDAO // custom DAO interface
private lateinit var db: AppDatabase
#Before
fun createDb() {
db = Room.inMemoryDatabaseBuilder(
ApplicationProvider.getApplicationContext(),
AppDatabase::class.java
).allowMainThreadQueries().build()
userDAO = db.userDAO()
}
#After
#Throws(IOException::class)
fun closeDb() {
db.close()
}
#Test
#Throws(Exception::class)
fun insertAndReadUser() {
val user = User(
1,
"123",
"Test Name",
"link.to/name/image#from_the.web"
)
userDAO.insert(user)
val inserted = userDAO.getByUID(1)
assertThat(inserted).isNotNull()
}
}
Throws the following error on the run log:
java.lang.RuntimeException: Delegate runner androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner for AndroidJUnit4 could not be found.
Caused by: java.lang.ClassNotFoundException: androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner
Here are the project dependencies:
dependencies {
def room_version = "2.2.6"
implementation "androidx.room:room-runtime:$room_version"
kapt "androidx.room:room-compiler:$room_version"
implementation "androidx.room:room-ktx:$room_version"
implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
implementation 'androidx.core:core-ktx:1.3.2'
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'com.google.android.material:material:1.2.1'
implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
implementation 'androidx.navigation:navigation-fragment-ktx:2.3.2'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.2'
implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.2.0'
implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'
implementation 'androidx.navigation:navigation-fragment-ktx:2.3.2'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.2'
testImplementation 'com.google.truth:truth:1.1'
testImplementation 'junit:junit:4.13.1'
testImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}
What could be causing this error and how to fix it?
Android Studio 4.1.1

I managed to find the issue.
In fact, I had put the testing file on the wrong folder, the [test] folder instead of [androidTest] folder. Moving the file to the correct folder managed to solve the issue.

Null pointer exception when stubbing

Good afternoon, I have a nullpointer exception when stubbing
package com.micheladrien.android.fresquerappel
import android.app.Application
import androidx.arch.core.executor.testing.InstantTaskExecutorRule
import com.micheladrien.fresquerappel.R
import org.junit.Before
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import org.mockito.Mock
import org.mockito.Mockito.`when`
import org.mockito.Mockito.mock
import org.mockito.junit.MockitoJUnitRunner
#RunWith(MockitoJUnitRunner::class)
class MainViewModelTest {
#Rule
#JvmField
var instantTaskExecutorRule = InstantTaskExecutorRule()
#Mock
val applicationMock: Application = mock(Application::class.java)
#Before
fun setUpTaskDetailViewModel() {
`when`(applicationMock.getString(R.string.collage_climat)).thenReturn("Climat")
}
}
edit : I need to stub the function when(applicationMock.getString(R.string.collage_climat)).thenReturn("Climat")
because my viewmodel will get strings from context.
According to this blog post : https://codepills.com/2018/05/10/3-basic-mistakes-for-nullpointerexception-when-mock/
I should replace when thenreturn by when then (answer) which if it's true, why ?
I have already Tested : Changing R.id value to a brut number. => Same error
Mocking the file inside the before and using lateinit for the declaration at #Mock => same error
Unlike previous question thread Mockito - NullpointerException when stubbing Method
I am directly stubbing the method. Not stubbing the method of the object of another method.
Any help would be greatly appreciated.
Edit : The VM I aim to test :
class MainViewModel(application: Application): AndroidViewModel(application), WaitingViewModel{
private val _name = MutableLiveData<String>().apply {
value = application.getString(R.string.collage_climat)
}
val name : LiveData<String> = _name
override fun notifyNewCollage(collage_name: String) {
_name.value = collage_name
}
}
Here is the gradle if you want to check the Mockito version :
dependencies {
implementation fileTree(dir: "libs", include: ["*.jar"])
implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
implementation 'androidx.core:core-ktx:1.3.2'
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'com.google.android.material:material:1.2.1'
implementation 'androidx.constraintlayout:constraintlayout:2.0.3'
def navigation_version = '2.3.1'
implementation "androidx.navigation:navigation-fragment-ktx:$navigation_version"
implementation "androidx.navigation:navigation-ui-ktx:$navigation_version"
implementation 'androidx.legacy:legacy-support-v4:1.0.0'
implementation "androidx.navigation:navigation-fragment:$navigation_version"
implementation "androidx.navigation:navigation-ui:$navigation_version"
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
implementation 'androidx.annotation:annotation:1.1.0'
implementation 'androidx.recyclerview:recyclerview:1.1.0'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
implementation 'il.co.theblitz:observablecollections:1.4.2'
def espressocore_version = '3.3.0'
androidTestImplementation "androidx.test.espresso:espresso-core:$espressocore_version"
androidTestImplementation "androidx.test.espresso:espresso-core:$espressocore_version"
androidTestImplementation "android.arch.core:core-testing:$lifecycle_version"
def mockito_version = '3.5.5' // For local unit tests on your development machine (also tested on 3.3.3)
testImplementation "org.mockito:mockito-core:$mockito_version" // For instrumentation tests on Android devices and emulators
androidTestImplementation "org.mockito:mockito-android:$mockito_version"
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test:rules:1.0.2'
}

Mockito advices against Mocking classes you don't own. So an Application mock is a bad idea.
Junit can give you the application context needed : https://developer.android.com/training/testing/junit-runner
For other info about stubbing fail, Mockito fails on stubbing : it tries to execute the function that should be stubbed

Unresolved androidx classes for writing unit tests

I am trying to write my first test and I have problem figuring out the right dependencies to get everything to work. Here is my test class
class EmployeeDatabaseTest {
private lateinit var employeeDao: EmployeeDAO
#Before
fun setup() {
EmployeeDatabase.TEST_MODE = true
employeeDao = EmployeeDatabase.getDatabase(??).employeeDao()
}
#Test
fun should_Insert_Employee_Item() {
val employee = Employee("xx", "xx", 31, Gender.MALE)
employee.id = 1
runBlocking { employeeDao.addNewEmployee(employee) }
val employeeTest = runBlocking { getValue(employeeDao.getEmployeeById(employee.id!!)) }
Assert.assertEquals(employee.name, employeeTest.name)
}
}
Normally I would obtain context by InstrumentationRegistry.getContext()...but InstrumentationRegistry can't be resolved. It also can't resolve getValue(..) method. I am new to testing but I bet is something with dependencies. Here is my build.gradle:
dependencies {
...
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.2.0'
androidTestImplementation 'androidx.test:rules:1.2.0'
androidTestImplementation 'org.hamcrest:hamcrest-library:1.3'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
androidTestImplementation 'androidx.test.uiautomator:uiautomator:2.2.0'
androidTestImplementation 'androidx.test:core:1.2.0'
androidTestImplementation 'androidx.test.ext:junit:1.1.1'
}
defaultConfig {
...
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
Do I miss something I am I doing something wrong?

A simple Context can be resolved with
androidx.test.core.app.ApplicationProvider.getApplicationContext()
which is part of the core module
androidTestImplementation 'androidx.test:core:1.2.0'
When you use Robolectric, you can also have it as
testImplementation 'androidx.test:core:1.2.0'

MutableLiveData is null in JUnitTest

I want to write a unit test. Therefore I need MutableLiveData. I started with a very basic test for setup but I cannot instantiate a MutableLiveData object. I is always null when I run the test. Do I have to mock anything? Any suggestions?
#RunWith(MockitoJUnitRunner.class)
public class DefaultLiveDataTest {
private static final int EXPECTED = 5;
private final MutableLiveData<Integer> underTest = new MutableLiveData<>();
#Test
public void exampleTest() {
underTest.setValue(EXPECTED); //underTest is Null
assertEquals(underTest.getValue().intValue(), EXPECTED);
}
}
java.lang.NullPointerException
at android.arch.core.executor.DefaultTaskExecutor.isMainThread(DefaultTaskExecutor.java:58)
at android.arch.core.executor.ArchTaskExecutor.isMainThread(ArchTaskExecutor.java:116)
at android.arch.lifecycle.LiveData.assertMainThread(LiveData.java:434)
at android.arch.lifecycle.LiveData.setValue(LiveData.java:279)
at android.arch.lifecycle.MutableLiveData.setValue(MutableLiveData.java:33)
at com.mypackage.DefaultLiveDataTest.test_that_live_data_has_default_value(DefaultLiveDataTest.java:22)
build.gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 27
defaultConfig {
applicationId 'com.mypackage.title'
minSdkVersion 16
targetSdkVersion 27
versionCode 1
versionName '1.0'
testInstrumentationRunner 'android.support.test.runner.AndroidJUnitRunner'
}
testOptions {
unitTests.returnDefaultValues = true
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support:design:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
implementation 'com.android.support:support-vector-drawable:27.1.1'
implementation 'android.arch.lifecycle:extensions:1.1.1'
implementation 'android.arch.lifecycle:viewmodel:1.1.1'
implementation 'android.arch.lifecycle:livedata:1.1.1'
annotationProcessor 'android.arch.lifecycle:compiler:1.1.1'
testImplementation 'junit:junit:4.12'
testImplementation 'org.mockito:mockito-core:1.10.19'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
annotationProcessor 'org.androidannotations:androidannotations:4.4.0'
implementation 'org.androidannotations:androidannotations-api:4.4.0'
compileOnly 'org.projectlombok:lombok:1.16.20'
annotationProcessor 'org.projectlombok:lombok:1.16.20'
}

Looks like you are missing the android.arch.core:core-testing dependency.
testImplementation "android.arch.core:core-testing:1.1.1"
This allows you to use the InstantTaskExecutorRule in your test, which will get rid of the isMainThread call.
https://developer.android.com/reference/android/arch/core/executor/testing/InstantTaskExecutorRule.html
#Rule
public InstantTaskExecutorRule instantTaskExecutorRule = new InstantTaskExecutorRule();

Add an executor InstantTaskExecutorRule() as a member of the Test class
A JUnit Test Rule that swaps the background executor used by the
Architecture Components with a different one which executes each task
synchronously. You can use this rule for your host side tests that use
Architecture Components.
//#RunWith(JUnit4::class) // For JUnit4
#ExtendWith(InstantExecutorExtension::class) // For JUnit5
class FilterViewModelTest {
#Rule #JvmField
val instantTaskExecutorRule = InstantTaskExecutorRule()
#Test
fun test() {
//Here you don't ask if isMainThread
}
}
build.gradle(:mobile)
android {
//...
dependencies {
//...
testImplementation 'androidx.arch.core:core-testing:2.1.0'
androidTestImplementation 'androidx.arch.core:core-testing:2.1.0'
}
}
GL
InstantTaskExecutorRule

I had this error and solved it by adding InstantTaskExecutorRule:
private lateinit var contactProfileViewModel: ContactProfileViewModel
private val getStatusesForContact: GetStatusesForContact = mockk(relaxed = true)
private val getStory: GetUserLastStory = mockk(relaxed = true)
private val successStatusesCaptor = slot<((List<StatusDomain>) -> Unit)>()
private val successStoryCaptor = slot<((List<StoryDomain>) -> Unit)>()
#get:Rule
val rule: TestRule = InstantTaskExecutorRule()
#Before
fun setUp(){
contactProfileViewModel = ContactProfileViewModel(getStatusesForContact, getStory)
}

Some error(s) occurred while processing annotations

When I add the code int activity
#Inject
lateinit var mCommonService:CommonService
The error comes
e: Error: Can't access Nullable
e: Can't find javax.annotation.Nullable
e: For details, please refer to the following stacktrace.
w: Warning: These options aren't used by any annotation processors:'[kapt.kotlin.generated]'
e: Some error(s) occurred while processing annotations. Please see the error messages above.
this is my module build.gradle
dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:25.3.1'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
testCompile 'junit:junit:4.12'
compile 'com.squareup.retrofit2:retrofit:2.3.0'
compile 'com.squareup.retrofit2:converter-gson:2.3.0'
compile 'com.jakewharton.retrofit:retrofit2-rxjava2-adapter:1.0.0'
compile 'com.squareup.okhttp3:okhttp:3.8.0'
compile 'com.squareup.okhttp3:okhttp-urlconnection:3.8.0'
compile 'io.reactivex.rxjava2:rxjava:2.0.1'
compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
compile 'com.google.dagger:dagger:2.11'
kapt 'com.google.dagger:dagger-compiler:2.11'
compile 'com.readystatesoftware.systembartint:systembartint:1.0.3'
compile 'com.google.code.gson:gson:2.7'
compile 'com.squareup.leakcanary:leakcanary-android:1.5.1'
// compile 'com.android.support:support-annotations:26.0.0-alpha1'
kapt "com.android.databinding:compiler:$rootProject.ext.gradle_version"
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}
This is my component
#ActivityScope
#Component(modules = arrayOf(CommonModule::class),dependencies = arrayOf(AppComponent::class))
interface CommonComponent {
fun inject(activity: MainActivity)
}
This is my module
#Module
class CommonModule {
#Singleton #Provides fun provideCommonService(retrofit: Retrofit): CommonService {
return retrofit.create(CommonService::class.java)
}
}
And this is my activity
#Inject
lateinit var mCommonService:CommonService// when i inject this,the error comes
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
getViewDataBinding(R.layout.activity_main)
DaggerCommonComponent.builder()
.appComponent(appComponent)
.commonModule(CommonModule())
.build()
.inject(this)
}
If I delete the inject code the program run correctly, I try add #JvmWildcard at CommomService #provides return type, but it still doesn't work