Add unit test using full rendering

  It processes all the descendent components.

  Issue: enzyme is not yet compatible with React 17
  ref: enzymejs/enzyme#2462

  How to check the React version on the project
  The package.json contains `"react": "^17.0.1",`
  ref: https://www.positronx.io/how-to-check-react-app-version-quickly/

react/testapp/src/test/appContent.test.js

@@ -1,6 +1,6 @@
 import React from "react";
 import Adapter from 'enzyme-adapter-react-16';
-import Enzyme, {shallow} from "enzyme";
+import Enzyme, {shallow, mount} from "enzyme";
 import App from "../App";
 import {ValueInput} from "../component/ValueInput";
 
@@ -10,4 +10,16 @@ it("Renders three ValueInputs", () => {
   const wrapper = shallow(<App/>);
   const valCount = wrapper.find(ValueInput).length;
   expect(valCount).toBe(3)
-});
+});
+
+it("Fully renders three inputs", () => {
+  const wrapper = mount(<App title="tester"/>);
+  const count = wrapper.find("input.form-control").length;
+  expect(count).toBe(3);
+});
+
+it("Shallow renders zero inputs", () => {
+  const wrapper = shallow(<App/>);
+  const count = wrapper.find("input.form-control").length;
+  expect(count).toBe(0);
+})