public final AssertSubscriber<T> assertError(){
  assertNotComplete();
  int s=errors.size();
  if (s == 0) {
    throw new AssertionError("No error",null);
  }
  if (s > 1) {
    throw new AssertionError("Multiple errors: " + s,null);
  }
  return this;
}

public final AssertSubscriber < T > assertError ( ) { assertNotComplete ( ) ; int s = errors . size ( ) ; if ( s == 0 ) { throw new AssertionError ( "No error" , null ) ; } if ( s > 1 ) { throw new AssertionError ( "Multiple errors: " + s , null ) ; } return this ; }
assert an error signal has been received .
