According to official google documentation we should add our test helpers for Architecture Components (LiveData) in a such way:
// Test helpers for LiveData
testImplementation "android.arch.core:core-testing:1.1.0"
And at least for me it just doesn’t work. (see the question above)
How it should be actually:
// Test helpers for LiveData
androidTestImplementation "android.arch.core:core-testing:1.1.0"
Now everything works just fine!