feature: tag tests; choose tags on command line

lib/src/runner/configuration.dart

Index: lib/src/runner/configuration.dart
diff --git a/lib/src/runner/configuration.dart b/lib/src/runner/configuration.dart
index bb28aeb87c926a81351280e218c615abd5278ca4..d0f406b7e70b41907a8634d66b23b74983507932 100644
--- a/lib/src/runner/configuration.dart
+++ b/lib/src/runner/configuration.dart
@@ -78,9 +78,15 @@ class Configuration {
     parser.addFlag("color", defaultsTo: null,
         help: 'Whether to use terminal colors.\n(auto-detected by default)');
     parser.addOption("tags",
+      abbr: 't',
       help: 'Comma-separated list of tags to run',
       allowMultiple: true,
       splitCommas: true);
+    parser.addOption("tag",
+      hide: true,
+      help: 'Same as --tags',
+      allowMultiple: true,
+      splitCommas: true);
 
     return parser;
   })();
@@ -135,7 +141,7 @@ class Configuration {
   final List<TestPlatform> platforms;
 
   /// Restricts the set of tests to a set of tags
-  final List<String> tags;
+  final Set<String> tags;
 
   /// The global test metadata derived from this configuration.
   Metadata get metadata =>
@@ -162,6 +168,13 @@ class Configuration {
       pattern = options['plain-name'];
     }
 
+    var tags = new Set<String>();
+    if (options['tags'] != null) {
+      tags.addAll(options['tags']);
+    }
+    if (options['tag'] != null) {
+      tags.addAll(options['tag']);
+    }
     return new Configuration(
         help: options['help'],
         version: options['version'],
@@ -177,7 +190,7 @@ class Configuration {
         pattern: pattern,
         platforms: options['platform'].map(TestPlatform.find),
         paths: options.rest.isEmpty ? null : options.rest,
-        tags: options['tags']);
+        tags: tags);
   }
 
   /// Runs [parse] on the value of the option [name], and wraps any
@@ -200,7 +213,7 @@ class Configuration {
           bool pauseAfterLoad: false, bool color, String packageRoot,
           String reporter, int pubServePort, int concurrency, this.pattern,
           Iterable<TestPlatform> platforms, Iterable<String> paths,
-          List<String> tags})
+          Set<String> tags})
       : pauseAfterLoad = pauseAfterLoad,
         color = color == null ? canUseSpecialChars : color,
         packageRoot = packageRoot == null
@@ -216,7 +229,5 @@ class Configuration {
         platforms = platforms == null ? [TestPlatform.vm] : platforms.toList(),
         paths = paths == null ? ["test"] : paths.toList(),
         explicitPaths = paths != null,
-        this.tags = tags == null
-            ? const <String>[]
-            : tags;
+        this.tags = tags;
 }