Gain insights into Jest, a versatile testing framework. Learn about fundamental and advanced testing techniques, from unit tests to CI/CD integration, for comprehensive JavaScript application testing.

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Jest is a framework for testing applications developed in JavaScript. It has a well-documented and well-maintained range of tools to run tests in parallel. It is simple and works with projects using Babel, TypeScript, Node, React, Angular, Vue, etc. It works well for both client and server testing. 

This course covers Jest in-depth and is agnostic of any specific JavaScript framework. The course begins with the fundamentals of Jest testing, deconstructing the components of a test and covering how to compose basic unit tests and snapshot tests with Jest correctly. Next, it shows the testing of asynchronous code and the code that relies on external dependencies. Lastly, this course illustrates how Jest testing can effectively integrate into the real-world software development cycle through CI/CD pipeline.

It gives you hands-on experience in setting up Jest, types of testing, testing coverage, mocking, and native tooling depth.

…. To come 

… to come 

Mastering Jest: A Complete Guide to Testing

# TypeScript configuration options

Jest is fully compatible with TypeScript applications, but there are a couple of nuances to this environment. We have two options for configuring Jest with TypeScript: `babel` and `ts-jest`. Unless an application is already using a `babel` configuration in its testing environment, we think that `ts-jest` is the more straightforward path.

## `ts-jest`

This package, available on our preferred package registry, is a TypeScript processor for Jest. All we need to do is start writing our test files as `.test.ts` instead of `.test.js` and change some things in our Jest configuration. First, we inform Jest that we will be using `.ts` (and any other TypeScript extensions we need, such as `.tsx`) for our modules. We can update the `moduleFileExtensions` field to reflect this:

```
{
  moduleFileExtensions: ['js', 'ts']
}
```
In addition, any other configurations that point to JavaScript files through paths or regex also need to account for the presence of TypeScript files. Therefore, let’s say we have the following code snippet:
```
{
  collectCoverageFrom: ['src/*.(js | jsx)']
}
```

We need to change this to the following:
```
{
  collectCoverageFrom: ['src/*.(js | jsx | ts | tsx)']
}
```
We also need to tell Jest to use `ts-jest` to process our TypeScript files. To do this, we add a key-value pair to the `transform` field whose key represents all TypeScript file extensions it can expect, and whose value is the package name:

```
{
  transform: {
    '\\.(ts | tsx)$': 'ts-jest'
  }
}
```

## `babel-jest`
If we’re already using a babel configuration inside our codebase (or want to), we can use this to enable TypeScript support.

Babel configuration for Jest requires several packages:

- `babel-jest`
- `@babel/core`
- `@babel/preset-env`

These can be installed using `yarn add --dev babel-jest @babel/core @babel/preset-env`.

Once these are installed, the app will need to have babel configured either through the `package.json` file or a separate `babel.config.js` file:



Learn how to use Jest for testing TypeScript applications.

Introduction

Setting Up Jest

Jest Matchers

Writing Unit Tests

Writing Snapshot Tests

Asynchronous Code

Mocking

Mocking External Libraries

Working with Jest Mocks

Setup & Teardown

Test Coverage & CI/CD Pipelines

Test Coverage in Jest

Conclusion

Bonus: Best Practices

Bonus: Resources for Continued Learning

Appendix

Jest and TypeScript

TypeScript configuration options

`ts-jest`