* ways similar to {@link FluentFuture}s:
 *
 * <ul>
 *   <li>by transforming the value from a successful input step,
 *   <li>by catching the exception from a failed input step, or
 *   <li>by combining the results of several input steps.
 * </ul>
 *
 * Each derivation can capture the next value or any intermediate objects for later closing.
 *

    nonePlusA.callStart(FailingCall())
    assertThat(a.takeEvent()).isInstanceOf<CallStart>()
    assertThat(a.eventSequence).isEmpty()
  }

  /** Make sure we didn't mess up our special case for combining aggregates. */
  @Test
  fun moreThanTwoAggregation() {
    val a = EventRecorder(enforceOrder = false)
    val b = EventRecorder(enforceOrder = false)
    val c = EventRecorder(enforceOrder = false)