anchor.diff:      }
       process = new Process.start(command.executable, command.arguments);
       process.onExit = exitHandler;
  -    process.onError = (error) { exitHandler(kErrorStartingProcess); };
       startTime = new Date.now();
       InputStream stdoutStream = process.stdout;
       InputStream stderrStream = process.stderr;
  
positive.code:   /** Which command of [testCase.commands] is currently being executed. */
    int currentStep;
  
    static final int kErrorStartingProcess = -171717;  // Chosen arbitrarily.
  
    RunningProcess(TestCase this.testCase,
        [this.allowRetries = false, this.processQueue]);
  
  
negative.code:    * the actual test and its output is analyzed in [testComplete].
     */
    void stepExitHandler(int exitCode) {
      process.close();
      int totalSteps = testCase.commands.length;
      String suffix =' (step $currentStep of $totalSteps)';
      if (currentStep == totalSteps) { // done with test command
  