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.

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Mastering Jest: A Complete Guide to Testing

## Synchronous vs. asynchronous

The words “synchronous” and “asynchronous” are likely used often when discussing programming. They describe an important part of how our code executes. In **synchronous programming languages**, such as Java and Python, a line or block of code does not begin to execute until the previous line or block in progress has been completed successfully. In other words, how we read the code reflects the order in which it runs. It’s fairly intuitive.

Asynchronous code execution is less intuitive. In an **asynchronous language**, other code can begin to execute while the previous code is still waiting to complete. This “other” code can potentially complete before the initial code. This early completion can lead to unintended consequences and a flow that cannot be relied upon.

This typically occurs with long-running processes and requests to external resources for data, i.e., an HTTP request. So, if a request is made, and the program is waiting for the response but not doing anything, subsequent code will continue to execute.



# Synchronous vs. asynchronous

The words “synchronous” and “asynchronous” are likely used often when discussing programming. They describe an important part of how our code executes. In **synchronous programming languages**, such as Java and Python, a line or block of code does not begin to execute until the previous line or block in progress has been completed successfully. In other words, how we read the code reflects the order in which it runs. It’s fairly intuitive.

Asynchronous code execution is less intuitive. In an **asynchronous language**, other code can begin to execute while the previous code is still waiting to complete. This “other” code can potentially complete before the initial code. This early completion can lead to unintended consequences and a flow that cannot be relied upon.

This typically occurs with long-running processes and requests to external resources for data, i.e., an HTTP request. So, if a request is made, and the program is waiting for the response but not doing anything, subsequent code will continue to execute.



Uncover the pitfalls of testing the asynchronous code with Jest.

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

The Problem

Synchronous vs. asynchronous