fix variable in catch statement

pkg/unittest/lib/html_individual_config.dart

 // Copyright (c) 2011, 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.
 
 /**
  * A unit test library for running groups of tests in a browser, instead of the
  * entire test file. This is especially used for large tests files that have
  * many subtests, so we can mark groups as failing at a finer granularity than
  * the entire test file.
  *
  * To use, import this file, and call [useHtmlIndividualConfiguration] at the
  * start of your set sequence. Important constraint: your group descriptions
  * MUST NOT contain spaces.
  */
 library unittest_html_individual_config;
 
 import 'dart:html';
 import 'unittest.dart' as unittest;
 import 'html_config.dart' as htmlconfig;
 
 class HtmlIndividualConfiguration extends htmlconfig.HtmlConfiguration {
-
-  String _noSuchTest = '';
-  HtmlIndividualConfiguration(isLayoutTest): super(isLayoutTest);
+  HtmlIndividualConfiguration(bool isLayoutTest): super(isLayoutTest);
 
   void onStart() {
     var search = window.location.search;
     if (search != '') {
-      try {
-        for (var parameter in search.substring(1).split('&')) {
-          if (parameter.startsWith('group=')) {
-            var testGroupName = parameter.split('=')[1];
-            unittest.filterTests('^$testGroupName${unittest.groupSep}');
-          }
+      var groups = search.substring(1).split('&')
+          .where((p) => p.startsWith('group='))
+          .toList();
+
+      if(!groups.isEmpty) {
+        if(groups.length > 1) {
+          throw 'More than one "group" parameter provided.';
         }
-      } catch (e) {
-        print('tried to match "$testGroupName"');
-        print('NO_SUCH_TEST');
+
+        var testGroupName = groups.single.split('=')[1];
+        var startsWith = "$testGroupName${unittest.groupSep}";
+        unittest.filterTests((unittest.TestCase tc) =>
+            tc.description.startsWith(startsWith));
+
+        if(unittest.testCases.isEmpty) {
+          throw 'No tests match group "$testGroupName".';
+        }
       }
     }
     super.onStart();
   }
 }
 
 void useHtmlIndividualConfiguration([bool isLayoutTest = false]) {
   if (unittest.config != null) return;
   unittest.configure(new HtmlIndividualConfiguration(isLayoutTest));
 }