# Jest configuration

First, go to the <mark style="color:purple;">package.json</mark> file. There, at the bottom of the file, we can see the <mark style="color:blue;">`jest`</mark> field with the configuration for it. Let's then cut this content and paste it into a new file we'll create at the root of the project: <mark style="color:purple;">jest.config.cjs</mark>.

{% hint style="info" %}
The extension <mark style="color:purple;">.cjs</mark> is basically the same as <mark style="color:purple;">.js</mark>, but enforcing **imports** as <mark style="color:blue;">`require()`</mark> (**CommonJS**), which is necessary for Jest here.
{% endhint %}

We should just change:

```javascript
"jest": {
  // Options
}
```

for:

```javascript
module.exports = {
  // Options
}
```

{% hint style="info" %}
In this case, we use a <mark style="color:purple;">.cjs</mark> (<mark style="color:red;">**JavaScript**</mark>) file because

* **JSON** would not allow for some function calls we'll make soon
* **TypeScript** would create a <mark style="color:purple;">src</mark> folder inside <mark style="color:purple;">dist</mark>, which would require adjustments, for instance, in the <mark style="color:blue;">`entities`</mark> and <mark style="color:blue;">`migrations`</mark> fields inside the <mark style="color:purple;">data-source</mark> file
  {% endhint %}

After that, save the file, and its syntax will automatically be adjusted from JSON to JS. And to fix the error, add the name of this file to the <mark style="color:blue;">`ignores`</mark> field in the file <mark style="color:purple;">eslint.config.mjs</mark>. Let's also already add another name that will be necessary soon.

```javascript
'jest.config.cjs', 'test/jest-e2e.cjs'
```

Then add the following imports at the top of the file:

```javascript
const { pathsToModuleNameMapper } = require('ts-jest');
const { compilerOptions } = require('./tsconfig.json');
```

And add the following fields below <mark style="color:blue;">`rootDir`</mark>:

```javascript
modulePaths: ['<rootDir>'],
moduleNameMapper: pathsToModuleNameMapper(compilerOptions.paths, {
  prefix: '<rootDir>',
}),
```

This will make sure that **Jest** resolves the paths correctly. However, unfortunately we cannot use that path in the <mark style="color:purple;">tsconfig</mark> for the domain's entities in that fashion anymore, so we'll have to use the <mark style="color:blue;">`paths`</mark> more explicitly.

```json
"categories/*": ["domain/categories/*"],
"orders/*": ["domain/orders/*"],
"payments/*": ["domain/payments/*"],
"products/*": ["domain/products/*"],
"users/*": ["domain/users/*"]
```

If we now run the same test, that error will no longer happen. However, a new one will appear, suggesting that the dependencies cannot be resolved. This one will be solved when we write the tests themselves.

Let's also already configure the **e2e** tests. So, let's alter the extension of the file <mark style="color:purple;">test</mark>/<mark style="color:purple;">jest-e2e.json</mark> to <mark style="color:purple;">.cjs</mark> too and use the same imports as the other file.

However, there will be a subtle difference: the path to access the <mark style="color:purple;">tsconfig</mark> file should go up a folder, so it should be <mark style="color:blue;">`'../tsconfig.json'`</mark>. Also, we should go to the <mark style="color:purple;">package.json</mark> file and change the script <mark style="color:blue;">`test:e2e`</mark> to make it use the correct extension, so it should have <mark style="color:blue;">`.cjs`</mark> at the end instead of <mark style="color:blue;">`.json`</mark>.

Then, back in the <mark style="color:purple;">jest-e2e.cjs</mark> file, put the following path at the start:

```javascript
const modulePath = '<rootDir>/../src';
```

So that we can put below <mark style="color:blue;">`rootDir`</mark>:

```javascript
modulePaths: [modulePath],
moduleNameMapper: pathsToModuleNameMapper(compilerOptions.paths, {
  prefix: modulePath,
}),
```

Now, relocate the file <mark style="color:purple;">test</mark>/<mark style="color:purple;">app.e2e-spec</mark> to a <mark style="color:purple;">domain</mark> folder we'll create in the same folder, and change the filename to <mark style="color:purple;">users.e2e-spec</mark>. In a future moment, we'll create the **e2e tests** for users here.

Lastly, let's install a package that will be very useful for **mocking**, and also the **faker** library to create **fake data** quickly.

```sh
yarn add -D jest-mock-extended @faker-js/faker
```

Now, before actually going to the tests themselves, let's just simplify the **users resource**.

<mark style="color:green;">**Commit**</mark> - Jest configuration