Adding all tracks, I guess

dart/hello-world/test/hello_world_test.dart

@@ -0,0 +1,8 @@
+import 'package:test/test.dart';
+import 'package:hello_world/hello_world.dart';
+
+void main() {
+  test("Say Hi!", () {
+    expect(new HelloWorld().hello(), equals("Hello, World!"));
+  });
+}