OSD600 - Adding Testing Tool

1. Lab8 requirement

Testing is an important part of developer's community, it helps programmers to test their code, detect unexpected bugs, etc.
In this lab, I will set up a testing framework called Jest to test my-ssg.

Jest is a JavaScript testing framework, it helps JS developers to ensure the correctness of their source code. Jest pays attention to simplicity and that is the reason I make use of it in my project.

2. Modification process

• Install Jest:

npm install --save-dev jest

• Add script for testing so you can run npm test to run all tests in the command line:

{
  "scripts": {
    "test": "jest --verbose"
  }
}

• Write tests:

My-ssg is divided into 6 modules but in this lab I just created testing for 3 modules namely generateHTML, readTextFile and readJson, the rest will be updated later on.

I created generateHTML.test.js, readTextFile.test.js, readJson files which contains all test cases for 3 modules I chose.

In generateHTML.test.js, I came up with some ideas to test the generateHTML(title, body, language, stylesheet, htmlContainer):

• Function should create a title.html file inside the specified folder or ./dist by default.
• Function will throw an error if the title is an empty string or is not passed to the function
• Function will use default value if language, stylesheet and htmlContainer are not passed to the function
• Function accepts empty value for language and stylesheet

Before turning these ideas into code, I need to require the function from generateHTML module:

const { generateHTML } = require("./generateHTML");

I will create test cases inside a describe block, I declare some const variables which can be reuse in some test cases (best practice is declare them locally in each test case):

describe("test generateHTML(title, body, language, stylesheet, htmlContainer)", () => {
  const title = "index";
  const body = "Hello World!";
  const lang = "en-CA";
  const stylesheet = "https://cdn.jsdelivr.net/npm/water.css@2/out/water.css";
  const htmlContainer = "./dist";
  const expectedPath = "./dist/index.html";

  // test cases...
}

And here is how the test case look like:

test("function should create new HTML file named ${title}.html inside the ${htmlContainer} folder", () => {
    expect(
      generateHTML(title, body, lang, stylesheet, htmlContainer)
    ).toStrictEqual(expectedPath);
  });


test("function should throw an error when title is an empty string", () => {
    try {
      generateHTML("");
    } catch (err) {
      expect(err).toEqual(
        new Error(chalk.bold.red("***title cannot be empty!***"))
      );
    }
  });

The logic to test readTextFile() and readJson() are very similar, I check how the function behaves when the arg is empty or it is not passed to the function.

To pass all created test cases, I need to make some small modifications to the original source code.

View my commit: 6313fab

3. Overall

Writing test is a painful process, you may never know how many more tests you need to write for a snippet code to make sure that you get all problems it may produce. However, writing good tests helps improve the quality of the source code so this skill is necessary for any programmer to achieve.

All in all, thank you for reading the post.

Happy coding!