An example of testing methods vs behaviours

AudioPlayer.kt

fun playArtist(artist: Artist) {
  if (artist != Artist.TAYLOR_SWIFT) {
    return IllegalArgException()
  }
  addToRecentlyPlayed(artist)
  player.play(artist.getRandomSong())
}

TestingBehaviour.kt

@Test
fun `play artist verify recently played list contains artist`() {
  val artist = Artist.TAYLOR_SWIFT
  val audioPlayer = getAudioPlayer()
  audioPlayer.playArtister(artist)
  
  assertThat(recentlyPlayedList.contains(artist)).isTrue()
}

@Test
fun `play artist verify current song belongs to the artist`() {
  val artist = Artist.TAYLOR_SWIFT
  val audioPlayer = getAudioPlayer()
  audioPlayer.playArtister(artist)
  
  assertThat(audioPlayer.getCurrentSong().artist).isEqualTo(TAYLOR_SWIFT)
}

@Test
@Throws(IllegalArgException)
fun `play with invalid artist expect IllegalArgException`() {
  val artist = Artist.MJ
  val audioPlayer = getAudioPlayer()
  audioPlayer.playArtister(artist)
}

TestingMethod.kt

@Test
fun `play artist verify recently played list and audio player state`() {
  val artist = Artist.TAYLOR_SWIFT
  val audioPlayer = getAudioPlayer()
  audioPlayer.playArtister(artist)
  
  assertThat(recentlyPlayedList.contains(artist)).isTrue()
  assertThat(audioPlayer.getCurrentSong().artist).isEqualTo(TAYLOR_SWIFT)
}