Implement Test Case

pubspec.yaml

@@ -17,3 +17,4 @@ dev_dependencies:
   build_test: ^0.10.3+1
   build_web_compilers: ^0.4.0
   test: ^1.3.0
+  mockito: ^3.0.0

test/service/configuration_service_test.dart

@@ -0,0 +1,30 @@
+import 'package:rules_of_living/src/Engine.dart';
+@TestOn('browser')
+
+import 'package:test/test.dart';
+import 'package:rules_of_living/service/configuration_service.dart';
+import 'package:rules_of_living/service/engine_service.dart';
+import 'package:mockito/mockito.dart';
+
+class MockEngine extends Mock implements Engine {}
+class MockEngineService extends Mock implements EngineService {
+  MockEngine _engine = MockEngine();
+  @override
+  Engine get engine => _engine;
+}
+
+void main() {
+  group("simulation speed", () {
+    ConfigurationService sut;
+    MockEngineService mes;
+    setUp(() {
+      mes = MockEngineService();
+      sut = ConfigurationService(mes);
+    });
+
+    test("speed changes propagate to engine", () {
+      sut.simSpeed = 312;
+      verify(mes.engine.stepsPerSecond=312);
+    });
+  });
+}