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Understanding the Difference Between Unit Testing and End-to-End Testing

kokou adzo

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Which testing approach to utilize is the first question that comes to mind when establishing a test automation testing strategy for an application. Unit testing and end-to-end testing are the two main and most popular testing techniques. Knowing their main distinctions will help you choose which to utilize.

Individual application code units are tested as part of the unit testing approach. The complete program is tested from the user’s perspective during end-to-end testing. We can accomplish this by mimicking the user’s routine tasks.

There are various kinds of bugs that users may run against. Some may display errors, some may offer inaccurate data, and others may need help with functioning or browser compatibility. We should choose between unit testing and end-to-end testing for your application based on the kind of bug.

Let’s examine the differences between unit and end-to-end testing in this post and when to apply each in automation testing to compare actual and predicted outcomes.

Unit Testing

Unit testing is the process of testing the smallest functional unit of code. Automation testing helps ensure the quality of the code, and it deserves to be an integral part of software development. The best practice is to write software as small functional units and then write a unique unit test for each. Functional testing involves white box testing, one of the types of cloud testing that deals with the testing of cloud-based SaaS, PaaS & IaaS applications.

When the code is still being developed, we write unit tests. It classically falls under the concept of white-box testing. This is because understanding the internal workings of the code is necessary for any white-box testing. Nevertheless, a unit test case’s scope is constrained. One code unit can be tested at a time. The interactions between various code units cannot be tested.

Types of Unit Testing

There are mainly two types of unit/individual test mechanisms. This means there are two ways to create and run unit test cases.

  • Manual testing
  • Automation testing

Manual testing may have a guidance document with step-by-step instructions for testing each feature. However, manual testing is almost obsolete for complex applications.

Most applications now rely on automation testing to test each unit of code. Several testing frameworks like JUnit and PHPUnit allow you to create tests. Selenium, AWS, TestSigma, Apache JMeter, CloudTest, and Watir are the most used cloud testing tools in the automation testing scenario. After creating unit tests with these frameworks, you can mock external dependencies and run these cases to determine if your logic works as expected.

These tools help you record your execution and generate detailed stack traces and error/success reports. In the CI/CD pipeline, the code is compiled every time you create a new pull request,  and the existing unit test cases are also executed along with the code. So you can determine if the new change contains a bug.

Advantages of Unit Testing

Writing unit test cases is primarily about sorting out the many logical components of the program and making sure each one behaves correctly on its own. Most of the bugs that we introduce are simply found using unit testing. Additionally, it enables us to lessen the effort needed to find flaws in complicated systems by automating the testing process. When current code is modified, it assists in preserving code coverage and identifying errors.

Unit Testing – Example

You have an online application for purchasing airline tickets. Then, this will have multiple modules, each with several classes and features. There will be a specific use for each of these features.

Assume you can obtain information on every flight within a specific budget. In this instance, the procedure ought to yield a list of all the flights on a particular day and route whose price is within the input price range. We can test this function as a single piece of code using automation testing and unit test cases.

Thus, these unit tests need to be executed in the CI/CD pipeline anytime it generates the code to verify the underlying code.

End-to-End Testing

Testing an application’s behavior and functions from start to end is known as end-to-end testing. It simulates the user behaviors and determines if the desired results are produced. E2E testing is done only after unit testing is completed.

End-to-end testing evaluates every part of the program, from its user interface design to the deep technical features. Both automation testing and manual E2E testing can be done. It is used to identify the fatal faults and errors in the software that don’t meet the planned outcomes.

E2E tests are classified as black box testing since the tester will be unaware of the functionality’s programming methodology. The main goal of the E2E test is to ensure that the user has met the needs of the business.

Types of E2E Testing

Depending on the applicability of the E2E test, there are two types:

Horizontal E2E testing

  • The horizontal E2E test method spreads horizontally in an application. E2E tests are mostly used in individual ERP applications.
  • For example, consider a web-based e-commerce application with components such as inventory, shipping information, accounts, product information, etc. Testing all these components in the application simultaneously is part of horizontal testing.
  • Therefore, we usually perform horizontal E2E testing at the end of the release period, when all subsystem-related changes have been made. Therefore, before moving to the testing part, we must set up the environment.

 Vertical E2E testing

  • Here, testing is done hierarchically in layers. We test every component layer from start to finish to ensure quality.
  • We use vertical E2E testing to test complex and critical application components. E2E testing strategies target components such as expensive computer systems that do not include user interfaces.
  • In the example above, we can test the main system using unit tests. We then test the payment processing and email subsystem before testing the website, database infrastructure, API, and user interface.
  • Because vertical E2E testing is granular, it typically follows behavioral, test-based, or continuous testing.

End-to-End Testing – Example

Let’s think about the earlier illustration. We have already tested the application code’s various logical sections. End-to-end automation testing is about testing the entire application from the user’s perspective. We can take this action once the functionalities are implemented in a testing environment.

The testers will observe the output while simulating user behaviors on the application. The new version is verified from the user’s point of view if we obtain the anticipated results. A few instances of user activities are selecting a button, completing a form, organizing or filtering data, etc. You can construct automated test cases to mimic such user activities using a variety of test frameworks.

Advantages of End-to-End Testing

Complex modern apps rely on both external and internal subsystems for their construction. These projects must be validated as a whole, not only as separate components. When interacting with the entire system, a subsystem may fail even though it passed the tests individually. Hence, you can ensure your application is ready for production by conducting end-to-end testing.

End-to-end testing offers the following primary advantages

  • It validates the general soundness of your application. It offers perspectives on the application’s performance in various user environments and evaluates your application overall.
  • By taking into account the interaction between subsystems and services, edge-to-edge testing increases the scope of the test.

Differences between Unit Testing and End-to-End Testing

The difference between unit testing and end-to-end testing is that unit testing ensures that functions or calculations that produce data, numeric values, or text strings work as intended. End-to-end testing ensures that buttons, forms, updates, links, and workflows work correctly.

Both unit and E2E tests can be carried out manually and through automation testing. It depends on the scenario and the project scope. Both unit tests and end-to-end tests serve their purposes and have a purpose. However, let’s look at their main differences.

 

Parameter Unit Testing End-to-end Testing

Test Scope

As mentioned, unit tests primarily focus on individual code units, while E2E automation testing tests the application from the user’s perspective. Running unit tests is easy, and we can run them on any version.

 

On the other hand, running a complete end-to-end test with an application takes time.

 

Test Type

One kind of white-box testing is unit testing. Understanding the internal workings of a functional program is necessary if you wish to apply a unit test to it. Contrarily, end-to-end testing falls within the category of black-box testing. These tests evaluate features that don’t require functional knowledge or coding by simulating user actions with the application.

 

Automation Testing Methodology

Unit tests are mostly automated ones we can integrate into the CI/CD pipeline. As soon as we release new code, all the code is compiled, and test cases are run to check for possible errors caused by the new change. E2E tests can be either manual or automated. We may use multiple frameworks for automation testing or conducting manual tests simulating user actions.

Test environment

Developers mostly create unit tests, so they use them on programming machines. On the other hand, after building subsystems, we perform end-to-end tests in a separate test environment.

 

Performers

Unit tests are performed by the developers who write them. Instead, a group of testers or QA bodies perform E2E tests in a dedicated environment.

 

Parallel drive

We can run unit test cases in parallel because they focus on individual code units and do not depend on each other. In comparison, end-to-end tests must be performed back-to-back.

Access to database and other resources

We usually skip dependencies in unit tests; therefore, they do not need access to resources. End-to-end tests usually require more resources because this test aims to verify that the entire system is working as intended.

Efforts for Automation Testing

We need less time and cost to create unit test cases than end-to-end tests. E2E tests are complex and involve many subsystems.

 

 

Which is better, unit testing or end-to-end testing?

Both Unit and E2E testing mechanisms are fairly different from each other. Unit testing is mainly used in applications where in-depth testing is required to discover intricacies in the code implementations. End-to-end testing is used in the areas where an abstract level of testing similar to black-box testing is carried out to check whether the business requirements and specifications meet the test case results. This E2E mechanism of automation testing is carried out from start to end.

Both the testing scenarios have their own merits and demerits. So, carrying out both testing methods in your application is better. Cloud testing can also be carried out to scale end-to-end testing further. One such platform that provides cloud testing and can be used for E2E testing is LambdaTest.

LambdaTest is an AI-powered test orchestration and execution platform that facilitates end-to-end testing by offering a comprehensive suite of features. It provides a scalable infrastructure for end-to-end testing scenarios with over 3000 browser environments, including various browser versions, operating systems, and real mobile devices. This extensive coverage allows testers to simulate real-world conditions, ensuring that web applications perform seamlessly across diverse user environments.

The platform supports manual and automated testing, enabling testers to run scripts and perform actions on real browsers hosted in the cloud. With features like parallel testing, testers can significantly reduce testing time by executing tests concurrently on multiple environments. LambdaTest also integrates with popular test automation frameworks, making it convenient for teams using tools like Selenium and Appium to leverage the platform’s capabilities. Overall, LambdaTest simplifies the complexity of end-to-end testing by providing a cloud infrastructure that allows testers to validate the entire user journey and detect potential issues before deploying applications to production.

Conclusion

In conclusion, each type of automation testing, unit and end-to-end test has a certain function. Including both of them in your testing procedures is always preferable.

Writing, maintaining, and comprehending unit test cases is very simple. However, because it’s a white-box testing method, creating unit test cases correctly requires that you comprehend the code. Furthermore, unit test cases cannot cover every functionality of the program.

Thus, a final end-to-end test before release is essential to ensure that every component of the application functions as planned and as a unit. They take a lot of time to complete, but they can be highly helpful in identifying problems and performance consequences before a production release.

 

Kokou Adzo is the editor and author of Startup.info. He is passionate about business and tech, and brings you the latest Startup news and information. He graduated from university of Siena (Italy) and Rennes (France) in Communications and Political Science with a Master's Degree. He manages the editorial operations at Startup.info.

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