feature: tag tests; choose tags on command line

lib/src/runner.dart

Index: lib/src/runner.dart
diff --git a/lib/src/runner.dart b/lib/src/runner.dart
index e5831e58a8d29d6d44921f6ec68b54ea8f9253df..260c3106951badc31a575aaecf285d2af02b05eb 100644
--- a/lib/src/runner.dart
+++ b/lib/src/runner.dart
@@ -158,8 +158,9 @@ class Runner {
       ]);
     })).map((loadSuite) {
       return loadSuite.changeSuite((suite) {
-        if (_config.pattern == null) return suite;
-        return suite.filter((test) => test.name.contains(_config.pattern));
+        return suite.filter((test) =>
+            (_config.pattern == null || test.name.contains(_config.pattern)) &&
+            (_config.tags.isEmpty || intersect(_config.tags, test.metadata.tags)));
       });
     });
   }