Add a task of webapp test (#51)

* Add a task of webapp test

* Flesh out tests

* Simplify test case

* Remove unnecessary dependency

* Fix style

* Add dependency

* Add trainling newline

webapp/src/manifest.test.js

@@ -0,0 +1,6 @@
+import {id, version} from './manifest';
+
+test('Plugin id and version are defined', () => {
+    expect(id).toBeDefined();
+    expect(version).toBeDefined();
+});