Exercise - Install packages

4 minutes

The developers at Tailwind Traders realize that they're about to put extensive resources into developing apps for the Node.js platform. These apps are going to need testing. After some analysis, they find that Node.js has limited testing capabilities. So they need to use a framework. They've found Jest in the npm registry. It seems to be widely used and promises to be a zero-config test framework. At this point, they just want you to install Jest, write a couple tests, and run them to see if Jest delivers on its promise.

Add a testing package by using the npm tool

You're given some code that parses an address from a string. Your task should be fairly straightforward. It involves installing the test framework, writing a couple tests, and running them.

Note

If you closed your terminal window after the previous exercise, you might need to set up your environment again. Open a terminal window, and clone the exercise repo by running the command git clone https://github.com/MicrosoftDocs/node-essentials/. You can ignore warning messages about the cloned folder already existing or the directory not being empty.

In your terminal window, change to the folder that has the cloned files for this exercise:
```
cd node-essentials/node-dependencies/5-exercise-dependency
```
In this folder, you should see two JavaScript files:
```
-| address-parser.js
-| package.json
```
Open the address-parser.js file. It should look like this file:
```
exports.parse = function parseOrder(order) {
  const match = order.match(/order:\s(?<order>\w+\s\w+).*address:\s(?<address>\w+\s\w+\s\w+).*payment info:\s(?<payment>\w+)/)
return match.groups;
}
```
This function takes a string and parses out information about what a customer orders, where it should be delivered, and how it will be paid for. We'll add Jest and write some tests for the function.

Close the address-parser.js file.
Install the Jest library by running this command:
```
npm install jest --save-dev
```
After the Jest library installs, open the package.json file and find the devDependencies section. You should see an entry that looks like this example:
```
"devDependencies": {
   "jest": "^28.0.0"
 }
```
Notice that the Jest library has an identified development dependency.
In the package.json file, find the scripts section. Replace the existing test action entry with the following code:
```
"test": "jest"
```
Save your changes and close the package.json file.
In the terminal, create a new folder named __tests__.

In the __tests__ folder, create a file named address-parser.js, and then add the following content to the file:

const { parse } = require("../address-parser");

describe('Address parser', () => {
  test('should parse correctly', () => {
    expect(
      parse(
         "I want to to order: 3 books to address: 112 street city here is my payment info: cardnumber"
      )
      ).toEqual({
        order: "3 books",
        address: "112 street city",
        payment: "cardnumber",
      });
  })
})

Save your changes and close the file.

Your project structure should now look like this example:

-| package.json
-| address-parser.js
-| __tests__/
---| address-parser.js

The test script checks the parsing ability of the address-parser.js function. The test ensures the function can correctly parse out the needed information.

Run the tests by entering this command in the terminal:

npm run test

You should get the following output:

Address parser
 ✓ should parse correctly (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.216 s
Ran all test suites.

Success! Your test passes, and you added testing by installing a dependency.

Congratulations. You successfully installed Jest as a dependency, wrote tests for application code, and ran the tests. Jest seems to deliver on its promise, and Tailwind Traders is likely to be happy with this evaluation.

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