What is mocha chai testing?

February 27,2021 - 8 min read
What is mocha chai testing?

Testing is a crucial part of the development process. In this blog, we are going to discuss two essential testing tools, chai and mocha. Before starting our blog about mocha chai testing, we are going to first discuss the importance of testing. We will understand why different types of tests are so necessary for the process of developing an application. Let’s begin the blog with the meaning and importance of Test-Driven Development commonly known as TDD.

What is Test-Driven Development?

Test-Driven Development is the name given to a process where it is required to write unit tests before the code. These unit tests rely on the repetition of a very short development cycle and the requirements change in different test cases. In this method, the code fails miserably at first and then after the developer writes clean code, the test cases are passed.

In simple terms, in the cycle, the developer first writes a test that fails surely because no code has been developed yet for these tests, the developers should actually check if the test cases fail. After this step, the next is when a programmer writes a clean code in order to pass the test cases. After this step, the developer should ensure if all test cases are passing are not, if test cases aren’t passed, they should reiterate and write better code in order to pass all test cases. The final aim should be to make our code better and more efficient and refactor it to create different test cases.

Now that we have talked enough about testing and Test-Driven Development in particular, it’s a good time to discuss chai and mocha testing. In short, Mocha is a JavaScript test framework that runs on Node.js and also on the ser and allows asynchronous testing along with the use of any assertion library. It tests coverage reports. The next testing tool we are going to talk about is Chai, which is a TDD assertion library for NodeJS and the browser. Chai can easily be paired with any Javascript testing framework. The basic difference between the two is that mocha is a framework whereas chai is a library. In the rest of the blog, we would discuss bot the testing tools in detail. Let’s begin with understanding mocha in little more detail.

Testing Using Mocha

In order to understand Mocha, it’s important to have a look at some of the most important terms regarding Mocha. Let’s get started!

The first is Describe () which is basically used to group. This allows nesting up to any level. Second is it () which is the basic test case. Before () is a hook that is run before it () or describe () whereas beforeEach () is run before each it () or describe (). Similarly, after () is run after it () or describe () and afterEach () is run after each it () or describe ().

Now that we have looked at some of the most important hooks used in regards with Mocha, it’s time we look at the different test cases and how.

In the t example of the test case, the only hook called is it () and mocha runs only this test. Moving to the next example, which is a nested test case where users nest some describes () hooks and then it () is called to execute the test.

There can be another test case in which the describe () hook contains two it () that execute the tests. In another example, users can only run once before the first test case is executed. In this case, mocha once executes the code inside the hook before (), this is executed before the first it ().

In another scenario, beforeEach () is executed every time the hook it () is encountered. For example, if there is one it (), beforeEach () is executed once, if there are two it (), it will be executed two times and so on. There is one last example of Mocha testing in which there are two tests in one big test as the hook describe () is nested and it () is executed.

In the examples above, we discussed some of the common scenarios of Mocha Testing. Let’s look at some more points that will help us better understand this particular testing tool.

As mentioned above, Mocha has a set of functions that are executed in a particular order and their results are logged in the terminal window. It is basically a framework for testing. The tests in Mocha generally use the keywords ‘describe’ and ‘it’ which provide structure to tests as they batch them into test suites or one unit test case.

The test suite refers to a group of tests relating to a single functionality or behaviour, whereas one unit test case describes the desired code that either passes or fails the test case. Another difference between test suite and test case is that the former is batched under ‘describe’ keyword and single test cases are coming under the ‘it’ keyword.

With Mocha, there are various tools that can clean the state of the software being tested. This also ensures that the test cases run independently of each other. One of the key principles of unit testing is the independence of test cases. If one test case fails, the reason behind the failure can be easily identified and hence the debugging process is quickened.

With this we have discussed the basic concept of Mocha testing and its different use cases. It is now time we dwell into Chai testing. Both of these are basically JavaScript frameworks that are generally used in coordination with each other for unit testing. Chai is basically used in Assertion and hence, in order to understand Chai, we need to first have a thorough understanding of assertion. In the next segment, we discuss the idea of assertion in test cases and then proceed to Chai testing. Let’s get started!

Assertions and Chai Testing

Assertions are the basic component of any test case and these test cases describe a behaviour. Assertions are related to a particular value and the test case fails if the expected value is not equal to the actual value. If the test case needs to be passed, it is mandatory for the assertion of the test case to be met.

Assertions are very important when it comes to testing and this is how Chai, an assertion library, comes into the picture. As mentioned above, Chai and Mocha are often used together.

Chai provides various functions and methods in a clean syntax that compares the output of a certain test with its expected value. Let’s look at the code of a Chai assertion. The code looks like thispect (KonfinityArray).to.have.lengthOf(9); This code above checks whether the variable KonfinityArray has a length of nine or not.

Chai is integral in the entire process of testing applications and software. We hope you are clear with the concept of both Chai and Mocha Testing and are ready to proceed to our next segment where we will discuss API testing using Chai and Mocha together.

Chai and Mocha Testing Using API

As we have already learnt the individual definitions of Chai and Mocha, it’s time to explore and make tests using chai and mocha using APIs. Let's get started!

The first step is to create the necessary files and folders and create $ touch tests/api.js in the same folder. After that, a new dependency by the name of chai-http has to be installed. This dependency makes requests from the server. Now, it’s also better to install express to avail its advantage. The code of the same looks like $ yarn add chai-http express or it can also be written as $ npm i chai-http express.

In our example, we will make a function that will create a server when the tests are being executed and would be closed after it. –exit mocha option is used to close the server at the end of the test cases. The complete code is - $ yarn mocha --exit tests/api.js

You should know that assertions run asynchronously as the end function is passed a callback. A mechanism is used to explain the particular framework used for testing that the callback is completed. If this step is not taken, the test cases pass without the assertions being checked. According to Mocha, the done callback signals that the callback has been completed and the assertions are verified.

With this, we have come to the end of our tutorial on Mocha and Chai testing. This is an important blog because testing itself is an integral part of software and application development. It’s essential for developers in the testing domain to write robust test cases that are accurate. The accuracy of the test case is displayed in failing and passing conditions. The test should fail if the particular feature that is being tested is not implemented properly. Test cases that erroneously pass are misleading and eventually lead to faulty code getting deployed. The other side is that the test cases pass if everything is working as expected.

We hope this blog helped you understand the theory of TDD and how you can implement it using chai and mocha.

If you have dedicated time reading this article, you would hopefully understand how you can make your development skills better and more efficient using different types, cases and tools for tests. Feel free to share with us what you think about this blog or if you have any doubts or queries regarding application development and testing.

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