Javascript doc

javascript/README.md

@@ -5,30 +5,160 @@
 
 [JavaScript](https://developer.mozilla.org/docs/Web/JavaScript) testing with [Jest](https://jestjs.io/)
 
+- [Show me the code](#show-me-the-code)
+  - [Implementation](#implementation)
+  - [Test](#test)
+- [Run this project using 🐳 docker](#run-this-project-using--docker)
+- [Run this project locally](#run-this-project-locally)
+
+## Show me the code
+
+### Implementation
+
+1. Create `HelloMessage` class in [HelloMessage.js](HelloMessage.js):
+
+```javascript
+class HelloMessage {
+  text = "Hello World!";
+}
+```
+
+2. Create `HelloConsole` class in [HelloConsole.js](HelloConsole.js):
+
+```javascript
+class HelloConsole {
+  print(text) {
+    console.log(text);
+  }
+}
+```
+
+3. Create `HelloApp` class in [HelloApp.js](HelloApp.js):
+
+```javascript
+class HelloApp {
+  constructor(helloMessage, helloConsole) {
+    this.helloMessage = helloMessage;
+    this.helloConsole = helloConsole;
+  }
+
+  printHello() {
+    this.helloConsole.print(this.helloMessage.text);
+  }
+}
+```
+
+4. Create main function in [Main.js](Main.js) that wraps it all together:
+
+```javascript
+const HelloMessage = require("./HelloMessage");
+const HelloConsole = require("./HelloConsole");
+const HelloApp = require("./HelloApp");
+
+const message = new HelloMessage();
+const console = new HelloConsole();
+const app = new HelloApp(message, console);
+app.printHello();
+```
+
+### Test
+
+Following [Jest > Getting Started](https://jestjs.io/docs/getting-started) guide ...
+
+1. Test `HelloMessage` in [HelloMessage.test.js](HelloMessage.test.js):
+
+```javascript
+describe("HelloMessage", () => {
+  it("should return hello world", () => {
+    const message = new HelloMessage();
+    expect(message.text).toBe("Hello World!");
+  });
+});
+```
+
+2. Test `HelloApp` in [HelloApp.test.js](HelloApp.test.js):
+
+```javascript
+// 2.1 Mock ./HelloMessage module
+jest.mock("./HelloMessage");
+// 2.2 Mock ./HelloConsole module
+jest.mock("./HelloConsole");
+
+describe("HelloApp", () => {
+  it("should print hello message", () => {
+    const messageText = "Hello Test!";
+
+    // 2.3 Set mock implementation to be returned
+    // anytime new HelloMessage() is called
+    HelloMessage.mockImplementation(() => {
+      return {
+        text: messageText,
+      };
+    });
+    // 2.4 Create a HelloMessage
+    // - It will be a mock thanks to 2.1 and 2.2
+    const message = new HelloMessage();
+
+    // 2.5 Create a HelloConsole
+    // - It will be a mock thanks to 2.3
+    const console = new HelloConsole();
+
+    // 2.6 Create a HelloApp, the one we want to test, passing the mocks
+    const app = new HelloApp(message, console);
+    // - Execute the method we want to test
+    app.printHello();
+
+    // 2.7 Verify HelloConsole mock has received one time
+    // a call to print() with "Hello Test!"
+    expect(console.print).toHaveBeenCalledTimes(1);
+    expect(console.print).toHaveBeenCalledWith(messageText);
+  });
+});
+```
+
+3. Test output should look like:
+
+```
+> jest
+
+ PASS  ./HelloMessage.test.js
+ PASS  ./HelloApp.test.js
+
+Test Suites: 2 passed, 2 total
+Tests:       2 passed, 2 total
+Snapshots:   0 total
+Time:        1.229 s
+Ran all test suites.
+```
+
 ## Run this project using 🐳 [docker](https://www.docker.com/)
-* Execute `./docker-run.sh`
-* Once inside the container:
-  * First time only, install dependencies with `npm install`
-  * Test with `npm test`
-  * Run with `npm start`
+
+- Execute `./docker-run.sh`
+- Once inside the container:
+  - First time only, install dependencies with `npm install`
+  - Test with `npm test`
+  - Run with `npm start`
 
 ## Run this project locally
 
 ### Pre-requisites
-* Install [Node.js](https://nodejs.org/en/) manually or ...
-  * Install [Node Version Manager](https://github.com/nvm-sh/nvm) and ...
-    * List available versions executing `nvm list`
-    * Install **Node.js** executing `nvm use v18` or `nvm use stable`
+
+- Install [Node.js](https://nodejs.org/en/) manually or ...
+  - Install [Node Version Manager](https://github.com/nvm-sh/nvm) and ...
+    - List available versions executing `nvm list`
+    - Install **Node.js** executing `nvm use v18` or `nvm use stable`
 
 ### Run locally
-* First time only, install dependencies with `npm install`
-* Test with `npm test`
-* Run with `npm start`
+
+- First time only, install dependencies with `npm install`
+- Test with `npm test`
+- Run with `npm start`
 
 ### Create project from scratch
-* Create project using `npm init`
-* Install [Jest](https://jestjs.io/) using `npm install --save-dev jest`
-* Configure scripts in [package.json](javascript/package.json):
+
+- Create project using `npm init`
+- Install [Jest](https://jestjs.io/) using `npm install --save-dev jest`
+- Configure scripts in [package.json](javascript/package.json):
   ```json
   "scripts": {
     "start": "node Main.js",