Observe LiveData in a test like you can with Rx test subscribers.

TestLiveData.kt

/** @author Aidan Follestad (@afollestad) */
class TestLiveData<T>(data: LiveData<T>) {

  private val receivedValues = mutableListOf<T>()
  private val observer = Observer<T> { emission ->
    emission?.let { receivedValues.add(it) }
  }

  init {
    data.observeForever(observer)
  }

  fun assertNoValues() {
    if (receivedValues.isNotEmpty()) {
      throw AssertionError("Expected no values, but got: $receivedValues")
    }
  }

  fun assertValues(vararg assertValues: T) {
    val assertList = assertValues.toList()
    if (!assertList.contentEquals(receivedValues)) {
      throw AssertionError("Expected $assertList\n\t\tBut got: $receivedValues")
    }
    receivedValues.clear()
  }

  @CheckResult fun values(): List<T> = receivedValues

  private fun List<T>.contentEquals(other: List<T>): Boolean {
    if (this.size != other.size) {
      return false
    }
    for ((index, value) in this.withIndex()) {
      if (other[index] != value) {
        return false
      }
    }
    return true
  }
}

@CheckResult fun <T> LiveData<T>.test() = TestLiveData(this)