anchor.diff:    void reportDivergence(
         TestResult result1, TestResult result2, bool outputDivergence) {
       numDivergences++;
  -    print('\n${isolate}: !DIVERGENCE! $version:$seed');
  -    if (outputDivergence) {
  +    print(
  +        '\n${isolate}: !DIVERGENCE! $version:$seed (output=${outputDivergence})');
  +    if (showStats && outputDivergence) {
         print('out1:\n${result1.output}\nout2:\n${result2.output}\n');
       }
     }
  
positive.code:   DartFuzzTest(this.env, this.repeat, this.trueDivergence, this.showStats,
        this.top, this.mode1, this.mode2);
  
    bool run() {
      setup();
  
      print('\n${isolate}: start');
  
negative.code:       await Isolate.spawn(run, this);
      }
      // Join.
      int divergences = 0;
      for (int i = 0; i < isolates; i++) {
        var d = await ports[i].first;
        divergences += d;
      }
      if (divergences == 0) {
        print('\nsuccess\n');
      } else {
        print('\nfailure ($divergences divergences)\n');
        exitCode = 1;
      }
    }
  
    static run(DartFuzzTestSession session) {
      int divergences = 0;
      try {
        final m1 = getMode(session.mode1, null);
        final m2 = getMode(session.mode2, m1);
        final fuzz = new DartFuzzTest(Platform.environment, session.repeat,
            session.trueDivergence, session.showStats, session.top, m1, m2);
        divergences = fuzz.run();
      } catch (e) {
        print('Isolate: $e');
      }
      session.port.send(divergences);
    }
  
    // Picks a top directory (command line, environment, or current).
  