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Unit Testing vs Integration Testing

Difference between unit and integration testing-ACCELQ
Posted On: 13 January 2024

Consumer demand for digital services has skyrocketed. Digital products necessitate continuous updates and enhancements. A single missed feature or improper code introduced to the software might cause the entire application to fail. Therefore, software testing is paramount.

According to Global Market Insights, the software testing market surpassed $40 billion in 2020, and it'll grow at a CAGR of 7% until 2027. After all, it ensures the quality of digital products and subsequently contributes to customer satisfaction. That's because properly tested applications establish reliability, strengthen security, and boost performance.

However, it's noteworthy that manual testing is no longer sufficient to meet the ever-increasing need for a quick turnaround. To keep up with demand, test automation is thorough-paced. Organizations adopt a multitude of automated tests that effectively lead to improved results.

And when we think of automation testing, unit tests are often the first thing that come to mind. They are, however, not the only ones. Many tools, like Selenium, make integration testing easier by automating defect detection in integrated components.

That said, unit and integration tests have their unique significance, whether manual or automated. This article will explain the distinction between these two forms of testing.

In essence, unit testing verifies logically separable blocks of code. On the other hand, integration testing ensures that all individual test units can work together. Individual members of the team write the code. They test their code independently. The components are then assembled and checked for integrated correctness.

What Is Unit Testing?

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Let us primarily learn the relevance of a unit in software testing. In short, a unit is the smallest independently executable block of code. As we test small blocks of code, the accuracy of the testing result increases. In essence, testing the smallest individual code block is called unit testing. It is also called component or module testing.

Concise checks provide a more detailed picture of how the code is working. It's noteworthy that unit tests adopt isolated testing. To that end, here's how it works:

  • The developer tests the unit of code.
  • They uncover and remove the bugs.
  • The defect is excluded from the defect monitoring system at an individual level.

What Is Integration Testing?

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Once the units are developed and tested by the developer, they're combined together. When tested as a whole, i.e., by joining together all components, the system is called integration testing. As a result, the integration tests come after the unit tests.

Integration tests assist software modules in working without errors. They synchronize the units or modules with one another, affirming that the connected units operate as a whole.

Integration testing conforms to the black box technique, which does not consider the internal structure of code. It will be hard to move up system testing effectively unless integration testing is carried out correctly.

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Let's Compare: Unit Testing vs. Integration Testing

As mentioned above, unit testing addresses isolated tests. Therefore, the scope remains limited to the input and output of one unit code block. Contrarily, integration testing combines the individual units and tests the validity as a whole. Let us now explore the major distinction between the two basic forms of testing.

Parameter Unit Testing Integration Testing
Fundamentals Isolated and individual testing of the smallest unit of code blocks Two or more units of application are integrated to test the working in combination
Testers Developers run unit tests Testers run integration tests
Complexity Low on complexity High on complexity since tests happens for multiple units together.
Testing Technique White Box Testing Black Box Testing
Order of Testing Primary Testing Performed after Unit Testing
Nature of Testing Unit tests involve Behavior Testing of the product Integration tests involve Logic Testing of the product
Scope The testing scope is limited The testing scope is broad
Dependencies The tests do not account for external dependencies The tests account for the code running with external dependencies
Error Detection Error detection remains easy with unit tests Error detection remains complex with integration tests

What Is the Similarity?

Software application testing requires both forms of testing to address the functional flaws. In fact, unit and integration testing are both forms of functional testing that need developers and testers to be familiar with the application's functionality.

Above all, a software application cannot suffice an efficient design without unit and integration tests. In short, each test can find coding flaws that the others overlooked. This gives developers the confidence to move forward with more automated tests that assess various levels of their application's functionality. In sum, both are fundamental and complement one another.

Advantages and Disadvantages of Unit Testing and Integration Testing

Unit testing is an expert in isolating and assessing individual components. Whereas Integration testing offers a holistic view by examining interactions between those components. Balancing both is key for efficient testing strategy in software development.

Unit Testing

Advantages:

  • Speed and Isolation: Unit tests are fast to execute as they focus on a single part of the application in total isolation, usually a single class or function. This isolation helps identify issues at the unit level quickly without interfering with other components.
  • Test-Driven Development (TDD): Unit testing is central to test-driven development, where tests are written even before implementation. It helps the development process with relevant test cases by aiming to meet all the specifications from the beginning.

Disadvantages:

  • Limited Scope: Unit tests can only test the functionality of units in isolation and might miss issues that arise from the interaction between different units or components.
  • Mocking Dependencies: While isolating units for testing, dependencies need to be mocked, which can sometimes lead to oversimplification and not catching issues that arise in a real-world scenario.

Integration Testing

Advantages:

  • Interactions and Side Effects: Integration tests focus on how different parts of the application work together, considering side effects that might be desirable or necessary to understand the system’s overall behavior.
  • Real-world Scenarios: By testing the integration of different components, these tests can uncover issues in the interaction between various application parts, providing a more realistic test scenario than unit tests.

Disadvantages:

  • Complexity and Speed: Integration tests are generally more complex and take time to execute than unit tests. Because they involve multiple components and require setting up and interacting with external systems like databases.
  • Obscuring Failures: Sometimes, mocking external resources in integration tests can cause failures by APIs. It might happen because of the components beyond the control of the application, leading to less clarity about the source of an issue.

When to Perform What?

We run the unit tests first. Integration tests cannot run without the unit tests in place. Once the developers test all components of an application, testers verify the integration success.

Please note that integration tests run after unit tests but before system tests. However, the drawback of integration testing is that it does not reflect the defect source. It becomes important to identify the discrepancies in the small blocks before we test the system as a whole. Moreover, it is easier to find a defect with unit testing than with integration testing.

Conclusion

To realize a comprehensive code coverage of an application, you need unit tests for executable lines of code. After that, integration tests are run to ensure that units function together cohesively. Favorably, you can achieve better overall code coverage with a robust test automation suite.

To sum up, it is critical to design an application that is bug-free and works in an intended manner. Therefore, one cannot choose one testing type over the other. Even though there is a distinction, teams must effectively execute the combination during the software development life cycle.

Nidhi Achhaa

Content Specialist at ACCELQ

Nidhi specializes in technology-based content and strives to create a unique, customized, and compelling piece with a flavor of SEO. A writer with a love for words and a storyteller at heart.

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