Jest Mock Functions in JavaScript| Frontend Development with Meta

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At this stage, you might be familiar with the concept of testing your code to make sure it's working as you intend it. You might also have come across some syntax of testing frameworks. But what about a language like JavaScript that has no built-in testing functionality? For JavaScript, you can use testing frameworks like Jest. Over the next few minutes, I am going to introduce you to the features of the Jest framework, code coverage, mocking, and snapshot testing. It is quite a mouthful. Let's get started. JavaScript doesn't have built-in objects or methods that would allow for tests to be written. Therefore, many different libraries have been built to tackle the issue of testing. Some examples of these libraries include Jasmine, Mocha, Karma, and qUnit. Then there is the one that you will cover now, namely the Jest testing framework. Jest is a JavaScript testing framework. It's often used for testing code like React, a JavaScript library maintained by Meta and a community of individual developers and companies. Besides plain JavaScript and React code just allows you to test Babel, TypeScript, Node, Angular, Vue, and various other frameworks. Jest also supports code coverage. Code coverage is a measure of what percentage of my code is covered by tests. If I say that I have an 80 percent code coverage, that means that only one-fifth of my entire code base is not covered by tests. But even 100 percent code coverage doesn't mean that you have tested for every conceivable expectation. It just means that there are some expectations tested for each line of my code. Still, code coverage is a handy tool to gauge the amount of my code base that's included in tests. The higher the code coverage, the lower the chance of having unidentified bugs. As a rule, the higher the percentage of code coverage, the lower the amount of time required to write new tests. This, however, depends on whether there are incomplete software requirements pending or if you are going to receive more requirements in the future. Next, let's cover the concept of mocking.

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