The example below shows a system that toggles the "favorite" state of a given job in the cache.

StateVsInteractionTesting.kt

// Unit under test.
fun toggleFavoriteForJob(job: Job) {
   if (job.isFavorite) {
   cache.unfavorite(job)
   } else {
   cache.favorite(job)
   }
}

// A unit test using interaction testing.
fun `toggle favorite with already favorited job verify job is unfavorited`() {
   // Test arrangements and setup.
   val job = getTestFavoriteJob()
   jobOperations.toggleFavoriteForJob(job)
   verify(cache).unfavorite(job)
}

// A unit test using state testing.
fun `toggle favorite with favorited job verify job is unfavorited`() {
   // Test arrangements and setup.
   val job = getTestFavoriteJob()
   jobOperations.toggleFavoriteForJob(job)
   assertThat(cache.getJobWithId(job.id).isFavorite()).isFalse()
}