Enable cached engine returns for EngineService

test/service/engine_service_test.dart

@@ -0,0 +1,19 @@
+@TestOn('browser')
+
+import 'package:test/test.dart';
+import 'package:rules_of_living/service/engine_service.dart';
+
+void main() {
+  EngineService sut;
+  setUp(() {
+    sut = EngineService();
+  });
+
+  test("EngineService creates an engine on demand", () {
+    expect(sut.engine, isNotNull);
+  });
+
+  test("EngineService returns the cached engine on subsequent requests", () {
+    expect(sut.engine, allOf(isNotNull, equals(sut.engine)));
+  });
+}