LiveDataTestObserver

LiveDataTestObserver.kt

import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import androidx.lifecycle.asLiveData
import kotlinx.coroutines.flow.Flow 

class LiveDataTestObserver<T> : Observer<T> {

    val observedValues = mutableListOf<T>()

    override fun onChanged(value: T) {
        observedValues.add(value)
    }
}

fun <T> LiveData<T>.test() = LiveDataTestObserver<T>()
    .also { observeForever(it) }

// Now we can do something like this:

@Test
fun `history pagination`() {
  coroutinesTestRule.testDispatcher.runBlockingTest {
    // Given
    val result = underTest.myLiveDataProperty.test()
    
    // When
    underTest.load()
    underTest.loadMore()
    underTest.loadMoreEvenMore()

    // Then
    assertThat(result.observedValues).containsExactly(
      listOf(record),
      listOf(record, record2),
      listOf(record, record2, record3),
    )
  }
}