Bugfix in test_runner: in certain cases tests did not get rerun

tools/testing/dart/test_runner.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 1706 matching lines @@
     var nextCommandIndex = testCase.commandOutputs.keys.length;
     var numberOfCommands = testCase.commands.length;
     Expect.isTrue(nextCommandIndex < numberOfCommands);
     var command = testCase.commands[nextCommandIndex];
     var isLastCommand = nextCommandIndex == (numberOfCommands - 1);
 
     void runCommand() {
       var runningProcess = new RunningProcess(testCase, command);
       runningProcess.start().then((CommandOutput commandOutput) {
         if (isLastCommand) {
+          // NOTE: We need to call commandOutput.unexpectedOutput here.
+          // Calling this getter may result in the side-effect, that
+          // commandOutput.requestRetry is set to true.
+          // (BrowserCommandOutputImpl._failedBecauseOfMissingXDisplay
+          // does that for example)
+          // TODO(ricow/kustermann): Issue 8206
+          var unexpectedOutput = commandOutput.unexpectedOutput;
           if (allowRetry && testCase.usesWebDriver
-              && commandOutput.unexpectedOutput
+              && unexpectedOutput
               && (testCase as BrowserTestCase).numRetries > 0) {
             // Selenium tests can be flaky. Try rerunning.
             commandOutput.requestRetry = true;
           }
         }
         if (commandOutput.requestRetry) {
           commandOutput.requestRetry = false;
           (testCase as BrowserTestCase).numRetries--;
           DebugLogger.warning("Rerunning Test: ${testCase.displayName} "
                               "(${(testCase as BrowserTestCase).numRetries} "
                               "attempt(s) remains) [cmd:$command]");
           runCommand();
         } else {
           completer.complete(testCase);
         }
       });
     }
     runCommand();
 
     return completer.future;
   }
 }