Solution: add databinding-compiler to androidTest configuration

[jonas-m-]

Since version 3.1 of Android Gradle plugin, you no longer have to include databinding-compiler as annotation processor, as the plugin does it for you.

Except it only does that for your main source configuration, not androidTest. For UI/instrumentation tests you still need to include the compiler yourself:

In your library module's build.gradle file:

apply plugin: 'kotlin-kapt'

dependencies {
    ...
    kaptAndroidTest 'androidx.databinding:databinding-compiler:3.3.2'
}