Extension function for "minutes ago" calendar formatting

CalendarUtils.kt

// run the code below on https://try.kotlinlang.org with JUnit env
class CalendarUtilsTests{
  @Test
  fun testUtilsClass(){
    val now = Calendar.getInstance()
    val threeMinutesAgo = now.clone() as Calendar
    threeMinutesAgo.add(Calendar.MINUTE, -3)
    assertEquals("3 minutes ago", "${threeMinutesAgo.minutesAgoFrom(now)} minutes ago")
  }

  fun Calendar.minutesAgoFrom(before: Calendar): Long {
    val diff = before.timeInMillis - this.timeInMillis
    return TimeUnit.MILLISECONDS.toMinutes(diff)
  }    
}