assertThat(formatDuration(  -999_500_000L)).isEqualTo(" -1 s ")
    assertThat(formatDuration(  -999_499_999L)).isEqualTo("-999 ms")
    assertThat(formatDuration(  -998_500_000L)).isEqualTo("-999 ms")
    assertThat(formatDuration(  -998_499_999L)).isEqualTo("-998 ms")
    assertThat(formatDuration(    -1_499_999L)).isEqualTo(" -1 ms")
    assertThat(formatDuration(      -999_500L)).isEqualTo(" -1 ms")

 */
fun formatDuration(ns: Long): String {
  val s =
    when {
      ns <= -999_500_000 -> "${(ns - 500_000_000) / 1_000_000_000} s "
      ns <= -999_500 -> "${(ns - 500_000) / 1_000_000} ms"
      ns <= 0 -> "${(ns - 500) / 1_000} µs"
      ns < 999_500 -> "${(ns + 500) / 1_000} µs"
      ns < 999_500_000 -> "${(ns + 500_000) / 1_000_000} ms"
      else -> "${(ns + 500_000_000) / 1_000_000_000} s "
    }