anchor.diff:    testCancelThrow();
     testCancelThrow2();
     testCancelThrow3();
  -}
  +  asyncEnd();
  +}
  
positive.code: void testCancelThrow() {
    asyncStart();
    asyncStart();
    StreamController c = new StreamController(onCancel: () {
      asyncEnd();
      throw "ERROR";
  
negative.code: }
  
  main() {
    asyncStart();
    testMultiController();
    testSingleController();
    testExtraMethods();
  