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Unit Testing vs Integration Testing

Dec 10, 2019
8 min read

Every software functions thanks to communication processes between modules. While a project team is working on the build release, knowing that the basic app blocks function well when put together is essential. That’s why tech companies run integration testing. 

As an alternative, there’s unit testing — it’s smaller in scale and cheaper, and allows to examine the product on the micro-level — unit by unit. 

Although these two approaches are complementary, it’s important to understand the difference between unit testing vs integration testing. In this post, you’ll find out what the objectives of both testing types are, their respective advantages, as well as unit test vs integration test example. 

What Is Integration Testing?

The integration testing definition refers to assessing the communication between separate software modules. Typically, the project team has to unit test the system before moving on to integration testing. In the software development life cycle, integration testing is the second step. 

The main aim of integration testing is to make sure the differences in logic patterns developers use when creating a module don’t compromise the connectivity of the system. There are several approaches to integration testing:

  • Top-down integration testing
    Is the practice of prioritizing the validation of complex, layered modules over low-level ones. In case one of the modules is not ready for testing yet, QA teams use stubs.
  • Bottom-up integration testing
    Is the opposite method to top-down integration testing. It implies validating basic modules first and integrating the complex ones later. The reasoning behind the approach is that it takes less time to create a low-level module — that’s why such components should be tested even when the more complex parts of the system are still in development.
  • Big bang
    If the testing team chooses this approach, it means that all modules will be tested simultaneously. QA specialists that execute tests by the big bang framework don’t test modules individually and instead wait until they are fully complete. Such a testing strategy is not the most efficient due to the high odds of missing major defects during testing.
  • Mixed (or sandwiched) integration testing
    Is a synchronized adoption of top-down and bottom-up practices. By following this approach, the testing team does not necessarily have to wait until either high- or low-level modules are fully coded, testing whichever of the two is ready.

Integration Testing Objectives

By conducting integration testing, teams aim to ensure that the system has no connectivity or communication issues on the level of software modules. If undetected, integration failures are difficult and expensive to fix after the product’s release as developers have to make in-depth system-level changes to remove these defects. 

After the integration testing process is complete, the testing team can focus on validating end-user journeys and usability.

The main integration testing objectives are follows:

  • Make sure that software modules work well when you integrate them together
    Integration testing ensures that the connectivity between modules meets the requirements specified by the testing plan.
  • Find interface errors
    During integration testing, both functional and non-functional interface components are validated. After completing a series of integration tests, the testing team should have full confidence in the performance of the software’s interface.
  • Ensure the synchronization between modules
    Integration tests help project teams ensure that software modules can function with no defects simultaneously and are fully synchronized with each other.
  • Fixes exception handling defects
    Exception handling mechanisms are crucial for high-assurance systems. Typically, such mechanisms are presented in most programming languages. However, QA teams need to ensure that the application is well protected against exception handling defects — integration testing helps pinpoint weak spots and red flags and mitigate the risks before the release of the final build.

Advantages of Integration Testing in Software Development

Integration testing in software testing is a must-have. It helps teams pinpoint weak spots and system defects at the early stages of development and promotes more confidence in the product. 

Here are some integration testing advantages:

  • Relatively fast testing process
    Although it takes more time to run integration tests, as opposed to validating separate system units, the process improves the speed and facilitates end-to-end testing.
  • High code coverage
    Integration testing has a wide scope, allowing QA specialists to test the entire system. The odds of missing out on a critical connectivity defect after a series of integration tests are slim. Other than that, the process is easy to keep track of.
  • Efficient system-level issue detection
    Integration testing falls under the definition of system-level testing since a tester has to combine modules and validate their joint performance. Later, the team will get a better look at the system’s overall performance by moving on to the next stage — system testing.
  • Detects bugs early as it’s run at the early stages of development
    Adopting integration testing allows the project team to pinpoint security and connectivity issues in the early stages of development. As such, integration testing offers developers superior control over the product and promotes the awareness of system vulnerabilities.

Unit Testing Definition

If you compare unit vs integration testing, unit testing is the first testing activity in the software testing life cycle. It’s a common practice for project teams to not involve testers in these stages, asking developers to perform unit tests instead. 

Unit testing does not require any specialized skills or well-trained workforce. Although there’s been much backlash regarding the high cost and inefficiency of unit tests, the approach has its own advantages. 

Units are the objects of unit testing — these are the smallest components of a tested system. As a software project typically consists of multiple units, automating unit testing is a popular practice among QA teams. 

The Objectives of Unit Test

In a nutshell, unit testing aims to separate system components and check their individual functionality. Other than the primary objective, the approach helps tech teams accomplish the following:

Find bugs early in the development cycle 

Unit testing allows introducing bugs and system defects early on in the development process. This way, the development team can resolve issues before integrating the units together and impacting the whole system. 

Use unit testing logs as documentation

The logs of unit testing will offer the project team a detailed description of the system on the micro-level. This testing method improves the interchangeability within the team since a newcomer developer can rely on logs provided by peers to be more familiar with the system. Unit testing provides a solid basic framework for understanding and handling APIs.

Improve the efficiency of code reuse

Unit tests improve code reusability since the reused units are well-tested. If the development team misses out on unit testing, the odds of reusing buggy code and spawning numerous system failures in the future increase dramatically. 

By testing the units beforehand, developers can be confident that there are no bugs or compilation issues, and that the written code fulfills its function according to business specification requirements. 

Validate the behavior of the system’s atomic behavioral unit

Missing out on unit testing will make other testing cycle stages considerably more challenging since the impact of system failures will have a higher magnitude and is likely to prevent the program from working altogether. 

Testing every unit of a system individually is a way to ensure that code-level bugs will not complicate integration or system testing. 

Advantages of Unit Tests in Software Development 

Unit testing is considered, by many teams, an unneeded addition to a tester’s busy working routine. Since it takes a while to unit-test the entire system, it’s common for tech project managers to skip the stage altogether. 

The truth is, unit testing should be integrated into the development routine since it’s relatively cheap and easy to perform. The advantages of the approach are numerous — here are but a few:

  • It lowers maintenance costs
    Testing early and often is a tried-and-true way to reduce the number of testing expenses. In our experience, fixing a bug in the early stages of development is about 4-5 times cheaper than coming back to it after the product is released.
  • Reduces uncertainty in the behavior of units
    Unit testing in software testing helps validate the performance of the basic code, offers a detailed description of a unit’s behavior in the shape of testing documentation and logs, and increases the confidence in the functionality of the backbone code among the tech team, as well as the acceptance of the system by the project stakeholders.
  • Helps detect changes that can break the design contract
    Other than helping maintain and change the code, unit tests help pinpoint the defects that break the design contracts. The testing method helps improve code design as a whole, encouraging developers to establish a uniform code interface and ensuring the test ability of every component.
  • Doesn’t require a highly skilled team of testers and can be conducted by developers
    When conducting unit testing, developers don’t have to manage multi-layered interfaces or write a complex test case. As a rule of thumb, most types of unit tests are executed in an automated testing environment and don’t require superior concentration from the testing team.

Difference Between Unit Testing and Integration Testing

As we compared unit and integration testing, it’s evident that both approaches have significant differences. To clarify the distinction between the two, take a look at the unit test vs integration test comparative table.

Unit testing

Integration testing

Validates the system unit-by-unit

Assesses the system as a whole by integrating several modules simultaneously

Fully autonomous — each unit is treated as a separate system

Connected since the testing team predominantly pays attention to the relationship between tested components

First level of software testing

Follows unit testing in the SLDR

No reliance on dependencies

Strongly relies on dependencies, involves the use of databases

Tests are faster to perform

Tests are slower

Usually performed by developers

Requires an experienced testing team

Is performed at the coding level

Is performed at the communication level

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Unit testing and integration testing are both a part of the software testing life cycle. The two share a common objective — detecting software defects as early on as possible. 

There’s a big difference between unit testing and integration testing. While the former approaches the system as a series of modules and examines the interactions and proper connectivity between them, the latter tests the product unit-by-unit. 

If you want to conduct both of these software testing types, reach out to PFLB. Our certified testers will bring forth the best testing practices to ensure your software is fully tested and the results are well-documented to avoid post-release bugs and defects. Take a look at the group of testing services our team offers. Leave us a message to discuss your idea and testing needs in detail — our account manager will reach out to you shortly.

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