Frontend-End Unit testing

Frontend testing

Front-end testing checks the presentation layer or user interface of a three-tier architecture of an application. In other words, we are testing the GUI - anything that is visible to the user on the client side. This involves testing functionalities like forms, inputs, menus, graphs, etc., along with their javascript functionality.

Source

Unit testing in the front-end is related to methods, properties, UI action elements, etc.

To create unit tests for the front-end, we must know what to test in our code. We should create test cases that resemble the functionality of our software.

Let’s take an example of an input box that considers both alphabet and digits as input and validate the inputs with boolean values. We have to write the test cases to check the input box's possible inputs.

// TEST 1: for only alphabets expect(alphanumericValidator('onlyAlphabets')).toBe(true);

// TEST 2: for only numbers expect(alphanumericValidator('123')).toBe(true);

// TEST 3: for both numeric and alphabets
expect(alphanumericValidator('alphabets123')).toBe(true);

These tests written above validate the logic of our code and check how the front-end works for the expected inputs. If the test is valid and possible, it returns a boolean value true; otherwise, it returns false.

• In the first case, we test the possible scenarios if the input box accepts only alphabets in the first case.
• In the second case, we test the possible scenarios of the input box if it accepts only digits or numbers.
• In the third case, we test the possible scenarios of the input box if it accepts both the alphabet and digits or numbers.

Now that we have written the unit test cases to check all the possible scenarios of an input box, let’s check the functionality of loops and branches.

// TEST 4: testing the else path for invalid inputexpect(alphanumericValidator('alpha123@@@@@@')).toBe(false);

// TEST 5: for special characters inputexpect(alphanumericValidator('#./')).toBe(false);

These tests above ensure that the user doesn’t give invalid characters or values other than alphabet and digits. This prevents us from encountering bugs and exceptions. This is an extension of the first test cases. The entire code must be tested similarly to ensure all the branches, statements, loops, conditions, etc., work as expected. 

Now we should test the error scenarios.  In unexpected input scenarios like null or undefined values, errors should be displayed in the corner cases to the user. This is important, especially for optional parameters.

// TEST 6, 7: for null/undefined input valuesexpect(alphanumericValidator(null)).toBe(false);
expect(alphanumericValidator(undefined)).toBe(false);

// TEST 8, 9: for empty strings or no input valuesexpect(alphanumericValidator('')).toBe(false);
expect(alphanumericValidator()).toBe(false);

This test verifies the code and makes it robust. It avoids crashing of application in case of unexpected inputs given by the user.

Why do we need the frontend to be unit tested?

Front-end testing is necessary for the developers and testers to analyze the software and its functionality from the user’s perspective. Most of the users do not know about the backend and the servers. All they notice is how responsive, attractive, and user-friendly our UI is. So to make their experience with our application smooth and effortless, the front-end needs to be tested.

The frontend unit testing:

• Identifies the performance issues of software from the user’s perspective.
• Verifies the application’s behavior and compatibility on multiple browsers and devices.
• Tests and validates the new releases, updates, and functionality.

Frameworks

There are many tools available for testers to perform front-end testing of any application or software. The frameworks mainly used for testing are:

• Mocha
• Jasmine
• Ava
• Jest
• Quint
• Karma
• SINON.js

FAQs

1. What is front-end unit testing?
   Front-end unit testing is a set of practices for testing the UI of an application or software. We test its functionality by writing unit tests for all the components, methods, forms, inputs, etc.
    
2. Does the front end need testing?
   Front-end testing is necessary for the developers and testers to analyze the software and its functionality from the user’s perspective. So to ensure a better experience for the user, the front-end needs to be tested too. 
    
3. Why is front-end testing important?
   Front-end Testing aims to test code functionality and verify whether a website or applications' presentation layer is bug or error-free. This has to be done after every release and updated to ensure that recent changes are properly implemented and functional.

Key Takeaways

Let’s briefly discuss the topics introduced in this article:

• Software testing is a technique used to examine the entire code in an application to check whether it produces the actual output and expected functionality to meet the user's requirements.
• The Unit testing comes under functional testing. It aims to segregate each part of a program into units and test those units individually to check the application's functionality.
• Front-end testing checks the presentation layer or user interface of a three-tier architecture of an application. In other words, we are testing the GUI - anything that is visible to the user on the client-side.
• Unit testing in the front-end is related to methods, properties, UI action elements, etc.

Hey Ninjas! Isn’t testing an exciting process? Explore more about testing and create your own test cases for your projects. Go through the web development course we suggest writing your test cases efficiently.

Happy Learning!