Cannot resolve symbol InstantTaskExecutorRule

I open example code BasicRxJavaSample (from this article Room+RxJava) The main thing is there:

@Rule
public InstantTaskExecutorRule instantTaskExecutorRule = 
    new InstantTaskExecutorRule();

And BasicRxJavaSample is all ok. But I can not apply this in my test. That's what's going on:

Cannot resolve symbol InstantTaskExecutorRule

And manual import does not work:

My autocompletion works like this

But should be so

My app build.gradle (full gradle here):

// tests
testImplementation 'junit:junit:4.12'
androidTestCompile "com.android.support:support-annotations:$supportVersion"
testImplementation "android.arch.core:core-testing:$archVersion"
// Test helpers for Room
testImplementation "android.arch.persistence.room:testing:1.0.0"
// https://github.com/mockito/mockito
testImplementation 'org.mockito:mockito-core:2.13.0'
androidTestImplementation 'org.mockito:mockito-android:2.13.0'
// AndroidJUnitRunner and JUnit Rules
androidTestImplementation 'com.android.support.test:rules:1.0.1'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
// https://developer.android.com/topic/libraries/testing-support-library/packages.html
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
androidTestCompile 'com.android.support.test.espresso:espresso-idling-resource:3.0.1'

Replace testImplementation by androidTestImplementation. So the tests on folder androidTest can have access to the library.

dependencies {
    androidTestImplementation "androidx.arch.core:core-testing:2.1.0"
}

> If you are not using androidx then use android.arch.core:core-testing:1.1.1

I know it's late but I would like to add one thing to this accepted answer.

If you want to use,

@Rule
public InstantTaskExecutorRule instantTaskExecutorRule = 
new InstantTaskExecutorRule();

in your JUnit test case, i.e., in test folder then use following dependency, i.e, with testImplementation

dependencies {
testImplementation "android.arch.core:core-testing:1.0.0"
}

If you want to use InstantTaskExecutorRule for your UI or integration test cases(androidTest folder), use androidTestImplementation. that is:

androidTestImplementation "android.arch.core:core-testing:1.0.0"

And if you want to add for both, use androidTestImplementation & testImplementation that is:

androidTestImplementation "android.arch.core:core-testing:1.0.0"

testImplementation "android.arch.core:core-testing:1.0.0"

For Android-X use below dependency:

androidTestImplementation 'androidx.arch.core:core-testing:2.0.0'

OR

testImplementation 'androidx.arch.core:core-testing:2.0.0'

for androidX migration, add

androidTestImplementation "androidx.arch.core:core-testing:2.0.0"

Please put this two dependencies in your gradle file,

dependencies {

    // Test helpers for LiveData
    testImplementation "android.arch.core:core-testing:1.0.0"

    // Test helpers for Room
    testImplementation "android.arch.persistence.room:testing:1.0.0"
}

Further information please go through this link, Android Architecture components integration guide

dependencies {
    testImplementation "androidx.arch.core:core-testing:2.1.0"
}

I think that there is a conflict in some of the linked libraries. I got around this, I used blockingGet() and blockingFirst().

and, in the end, I used https://developer.android.com/training/testing/junit-runner.html#using-android-test-orchestrator

androidTestUtil 'com.android.support.test:orchestrator:1.0.1'

this is what you need!

Sometimes test dependency issues can be an issue of selecting the appropriate build variant, depending on your Gradle configuration. In my case, tests are configured for the debug build variant only.