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

## Using `async/await`

The most modern handling of asynchronous code in JavaScript uses the `async` and `await` keywords. It doesn’t replace promises per se, but it is the syntactic sugar while working with promises.

With `async/await`, we mark a function as being asynchronous with the `async` keyword, which then allows us to `await` the completion of lines of code, like a request. JavaScript then knows to expect a promise from the call and awaits either its resolution or rejection.

## Jest and `async/await`

Working with this syntax in Jest is extremely intuitive. We can essentially use it the same way we do in our code. If a test suite or test is going to run asynchronous code, we just mark the anonymous function passed in as the second argument with `async` and then can use `await` inside of the anonymous function. The await keyword should only be used directly inside the function marked as `async`, at the top level. For instance, if a function will be awaited inside a `test` block, the anonymous function passed to `test` should be marked `async`, not the anonymous function passed to its parent `describe` block.

In the example below, we have a call to a cat facts API that uses the `async/await` syntax. We also have two testing files. In `asyncAwaitFail.test.js`, we incorrectly denote our `async` code by placing the keyword in our `describe` block rather than our `test` block.

In the second test file, `asyncAwait.test.js`, we place the `async` keyword in the argument passed to `test`, and are able to successfully await the API call. When `awaited` properly, we can access the response and make our assertions upon it.

In the output for these test files, we see a very large error stemming from the incorrect syntax in `asyncAwaitFail.test.js`. Below this error, we can see that one of the two tests failed, but one of the two tests passed:

# Using `async/await`

The most modern handling of asynchronous code in JavaScript uses the `async` and `await` keywords. It doesn’t replace promises per se, but it is the syntactic sugar while working with promises.

With `async/await`, we mark a function as being asynchronous with the `async` keyword, which then allows us to `await` the completion of lines of code, like a request. JavaScript then knows to expect a promise from the call and awaits either its resolution or rejection.

# Jest and `async/await`

Working with this syntax in Jest is extremely intuitive. We can essentially use it the same way we do in our code. If a test suite or test is going to run asynchronous code, we just mark the anonymous function passed in as the second argument with `async` and then can use `await` inside of the anonymous function. The await keyword should only be used directly inside the function marked as `async`, at the top level. For instance, if a function will be awaited inside a `test` block, the anonymous function passed to `test` should be marked `async`, not the anonymous function passed to its parent `describe` block.

In the example below, we have a call to a cat facts API that uses the `async/await` syntax. We also have two testing files. In `asyncAwaitFail.test.js`, we incorrectly denote our `async` code by placing the keyword in our `describe` block rather than our `test` block.

In the second test file, `asyncAwait.test.js`, we place the `async` keyword in the argument passed to `test`, and are able to successfully await the API call. When `awaited` properly, we can access the response and make our assertions upon it.

In the output for these test files, we see a very large error stemming from the incorrect syntax in `asyncAwaitFail.test.js`. Below this error, we can see that one of the two tests failed, but one of the two tests passed:

Learn how to use Jest to test asynchronous code with async/await syntax.

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

Testing with Async/Await

Using `async/await`

Working with Jest Mocks

Test Coverage in Jest

Testing with Async/Await

Using async/await

Using `async/await`