Update the semantics of the 'special-command' flag given to the test script.

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 76 matching lines @@
            this.completedHandler,
            this.expectedOutcomes,
            {this.isNegative: false,
             this.info: null}) {
     if (!isNegative) {
       this.isNegative = displayName.contains("negative_test");
     }
 
     // Special command handling. If a special command is specified
     // we have to completely rewrite the command that we are using.
-    // We generate a new command-line that is the special command
-    // where we replace '@' with the original command.
+    // We generate a new command-line that is the special command where we
+    // replace '@' with the original command executable, and generate
+    // a command formed like the following
+    // Let PREFIX be what is before the @.
+    // Let SUFFIX be what is after the @.
+    // Let EXECUTABLE be the existing executable of the command.
+    // Let ARGUMENTS be the existing arguments to the existing executable.
+    // The new command will be:
+    // PREFIX EXECUTABLE SUFFIX ARGUMENTS
     var specialCommand = configuration['special-command'];
     if (!specialCommand.isEmpty()) {
       Expect.isTrue(specialCommand.contains('@'),
                     "special-command must contain a '@' char");
       var specialCommandSplit = specialCommand.split('@');
       var prefix = specialCommandSplit[0].trim();
       var suffix = specialCommandSplit[1].trim();
       List<Command> newCommands = [];
       for (Command c in commands) {
-        var newExecutablePath;
+        // If we don't have a new prefix we will use the existing executable.
+        var newExecutablePath = c.executable;;
         var newArguments = [];
 
         if (prefix.length > 0) {
           var prefixSplit = prefix.split(' ');
           newExecutablePath = prefixSplit[0];
           for (int i = 1; i < prefixSplit.length; i++) {
             var current = prefixSplit[i];
             if (!current.isEmpty()) newArguments.add(current);
           }
           newArguments.add(c.executable);
         }
-        newArguments.addAll(c.arguments);
+
+        // Add any suffixes to the arguments of the original executable.
         var suffixSplit = suffix.split(' ');
         suffixSplit.forEach((e) {
           if (!e.isEmpty()) newArguments.add(e);
         });
+
+        newArguments.addAll(c.arguments);
         final newCommand = new Command(newExecutablePath, newArguments);
         newCommands.add(newCommand);
         // If there are extra spaces inside the prefix or suffix, this fails.
-        Expect.stringEquals('$prefix ${c.commandLine} $suffix'.trim(),
-            newCommand.commandLine);
+        String expected =
+            '$prefix ${c.executable} $suffix ${Strings.join(c.arguments, ' ')}';
+        Expect.stringEquals(expected.trim(), newCommand.commandLine);
       }
       commands = newCommands;
     }
   }
 
   int get timeout {
     if (expectedOutcomes.contains(SLOW)) {
       return configuration['timeout'] * SLOW_TIMEOUT_MULTIPLIER;
     } else {
       return configuration['timeout'];
@@ skipping 1075 matching lines @@
         // the developer doesn't waste his or her time trying to fix a bunch of
         // tests that appear to be broken but were actually just flakes that
         // didn't get retried because there had already been one failure.
         bool allowRetry = _MAX_FAILED_NO_RETRY > _progress.numFailedTests;
         new RunningProcess(test, allowRetry, this).start();
       }
       _numProcesses++;
     }
   }
 }