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Integration testing

Integration Testing Explained: Examples, Approaches and Challenges

Integration testing is integral to a successful testing strategy during software testing activity in the development lifecycle. There are four main testing types, integration, unit, acceptance, and system testing. Integration testing is crucial because it validates the integrity of the entire application before more diligent system testing.

This article will clearly define integration testing and detail the different integration testing types. It will introduce you to integration testing best practices, provide insight into some challenges you may encounter, and provide examples of integration test scenarios.

The article also includes a handy FAQ section to answer the most pressing questions about this type of testing.

Integration Testing

What is Integration Testing?

An integration test is a software module test. It includes software modules integrated logically and tested as a group instead of as individual units.

Each piece of software typically consists of several integrated modules coded by individual developers. Since the developer's understanding and programming logic may vary, their understanding of how modules integrate may not align. It makes integration tests a crucial part of the software testing process.

There are various methods of system integration testing, including big bang and incremental integration testing, with three sub-approaches to incremental testing.

The difference between unit testing and integration testing

Software comprises separate software modules or components that require different types of testing, including first-level testing (unit testing) and second-level testing, which includes integration testing.

Integration and unit testing are both types of functional testing and are critical for eliminating functional issues. Both require coding and a testing team that's knowledgeable about the coding. Both types of testing require similar types of functional testing tools.

While unit testing validates the software system against functional requirements and specifications, integration testing looks at integration scenarios covering the compatibility and synchronicity of software modules and components with one another.


Integration Testing Objectives

The main goal is to ensure that logically related modules are tested for their ability to work together efficiently with pertinent test data and as per the predefined criteria of the test plan. It is also to:

  • Ensure smooth integration between logically related modules and third-party tools.

  • That the interaction between modules and third-party tools is tested to ensure that the data accepted by the API is correct and that the correct response is generated.

  • Critical modules are tested on a priority basis.

  • To minimize exception handling defects before the final release.

  • To fix existing exception handling defects.

  • To pinpoint weak spots and red flags.

Advantages of Integration Testing

Here are some of the main advantages of integration testing techniques:

#1. It can be time-efficient

If you use both the top-down approach and bottom-up integration testing, it's the most time-efficient method. It also makes it possible to prioritize high-risk critical modules on the top or bottom.

#2. It's an independent testing process

You don't need to wait for lower-level modules to be available and unit-tested. As soon as the relevant modules are ready for testing and the test data and test cases are prepared, QA can start with integration testing.

#3. High code coverage

Integration testing allows a thorough analysis of the entire system's integrated units. The chance of missing out on crucial issues with this approach to testing is practically zero.

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#4. Early bug detection

With integration testing, the testing team can detect defects and security issues early in the software testing life cycle. The integration testing phase saves time and gives the development team more control over the final release.

An Integration Testing Example

To understand how integration testing works, here is a real-life testing scenario:

Testing a Mail Application

A mail application typically has modules like a login page, a mailbox module, and a module to delete the mail. Instead of testing the functionality of the individual modules, these modules are tested by how they are interlinked.

For example, how the mailbox page links with the delete module or how the login page links with the mailbox page.

There's no need to verify the functionality of each module; it's about how all the modules work together when interlinked. To check the integration between different modules, here are potential steps:

To check the link between the login and mailbox module:

  1. Enter login credentials, and click on the login button.

  2. Check if you are directed to the mailbox.


To check the link between the mailbox and delete mails module:

  1. From the mailbox module, select an email.

  2. Click the delete button.

  3. Navigate to the deleted/trash folder to check if the deleted email appears there.

Types of Integration Testing

The main integration testing types are:

Big Bang Testing

Big bang testing is used when all the application's components or modules are available. Once the development of all the modules is complete, they are integrated and tested together in one go. Because of the sheer volume of big bang integration testing, it's usually more suited for testing compact programs.

This type of integration test only requires minor planning. It's convenient for testing small systems and covers all the components, including critical modules. Some of the disadvantages of this type of testing are:

  • Every software module has to be completed for this approach, so the testing team remains extremely time-bound from when the integration testing starts until it ends.

  • Simultaneous testing means that high-risk or critical modules and peripheral modules are tested together with no priority.

  • Fault localization is complicated in this method, so it's not recommended for large-scale systems.

Incremental Integration Testing

Incremental testing involves bottom-up integration testing, top-down integration testing, or hybrid integration testing. In other words, testers work through the critical modules from front to back, back to front, or a combination of both to ensure consistency. It is a slightly more complex integration testing than the big bang approach.

The Bottom-Up Approach

With this approach, testers execute testing from the bottom up. They use it to identify crucial flaws in the application's lower-level modules.

The tester starts running integration tests from the bottom of the application's control flow and moves up from there. Suppose the development team still needs to complete some of the modules at the upper stage, but you are already testing lower-level modules. Then you can use suitable drivers to simulate the missing modules. 

Unlike the big bang testing approach, there's no time wasted. Developers and test teams can work together simultaneously, developing and running test cases to meet specifications. Fault localization is significantly more straightforward because it's based on the application's control flow.

Some of the disadvantages of the bottoms-up approach are:

  • You only test top-level control flow modules at the end of the testing.

  • It's impossible to create an early prototype; there's no room.

  • You have to create test drivers for all the modules except top-level modules.

  • You can only identify defects between interfaces at the end of the testing cycle.

black box testing

Top-down approach

Top-down integration testing follows the natural control flow hierarchy. For example, a meal planning app with four modules - a login page, a profile page, a meal plan page, and a payment page. To test the app with this approach, the test team would start at the top-level modules, i.e., the login page. If modules are missing, testers would use stubs and drivers as dummy programs.

This approach makes fault localization easier, and you'll have early prototype access. All the critical modules are tested first, which will reveal any significant design faults early in the testing environment.

The most significant disadvantage of the top-down approach is that lower-level modules lack attention in this approach.

Sandwich testing/hybrid testing

The hybrid testing method combines top-down testing with bottom-up testing. With this strategy, you can test lower-level modules and top modules together using stubs and drivers, which act as substitutes for missing modules. Sandwich testing is an excellent option for projects with several subprojects.

The benefits of sandwich testing are that test teams can simultaneously perform top-down and bottom-up testing. It is ideal for large-scale applications. Some of the disadvantages of this approach are:

  • It's more expensive than other approaches.

  • It is not suitable for smaller applications.

  • It requires testers with unique skill sets.

software developers

Integration Testing Tools

A wide variety of integration testing tools are available to software testing teams. These tools can boost efficiency and simplify integration testing techniques, making web-based application testing a breeze.

The right testing tool for your company would depend on your organization's requirements, including:

  • The programming language you use.

  • The project specifications.

  • Your test team's preferences.

  • Whether it supports multiple protocols like HTTP, SOAP, and JMS.

  • If it provides code coverage analysis.

Talk to us at Scriptworks about integration testing tools and our tailored testing solutions.

Challenges of Integration Testing

Despite all the advantages of integration testing, things sometimes go differently than planned. Various factors could make integration testing a little more challenging than you may expect, for example:

  • When many different developers with different styles work on the same project, the programming logic can become convoluted.

  • Many factors can complicate the testing, for example, the platform and environment the application is run on and the interaction with databases.

  • When you integrate two legacy systems or a new system into an existing system, it's rarely seamless.

  • When different teams develop two systems that have to be integrated, they may be incompatible.

how to test mobile app manually

Best Practices

To get the best out of integration testing, here are some best practices and tips to observe:

Start testing as early as possible

The traditional waterfall test process is to complete unit testing before integration testing. However, bug fixes later in the development cycle can become costly. With modern methodologies, it's possible to begin testing earlier.

When you perform integration testing earlier, detecting and fixing issues is easier as you progress through the development life cycle. It makes sense to begin fixing bugs when two or more modules are complete without waiting for developers to finish the entire application.

Not all modules have to be unit-tested. If there are under-developed or missing modules, simply replace them with stubs and drivers.


Keep integration tests and business logic separate

Unit testing is quick and shorter to run, so you can run it continuously for every build. The goal is to detect and correct bugs in code based on business logic. On the other hand, integration testing takes longer, and it covers integration, not business logic.

If you include this type of testing in every build, it will result in significant time consumption. Therefore, running it with every build is unnecessary.

Log extensively when you perform integration testing

Compared to unit testing, analyzing the origin of the defect revealed in integration testing is more complex. You will be testing the interaction between several modules, so integration testing's scope is extensive.

Because of this, it's crucial to log test results thoroughly during integration testing. It's the only way to uncover the root problem. Consider using a logging framework to provide detailed information after each test completion while also recording the software's performance.

Prepare test data and test cases thoroughly

The integration test plan document is a crucial part of the process. To create an effective plan, start by studying the software's architecture and app design. It will help you prioritize modules and their combinations correctly.

Create a clear test strategy with test data and test cases outlined in it. All test team members should find the information easy to understand and apply. Write test cases to cover all interface features and prepare mock data before you start. Don't select test data on the go; you should include it in the planning phase.

Keep project documentation handy and updated

Once your testing strategy and test plan document is clearly defined, keep it close. If there is any uncertainty about functionality, ask developers to explain it and ensure that the documentation is updated with further information or clarification.

Ensure that all the modules are checked

Before beginning integration testing, ensure all the relevant modules have been checked and are ready to be tested. If any modules are missing, replace them with stubs and drivers that simulate functionality.

test pyramid model

Consider automation

Software testing has come a long way in recent years, and some incredible automated tools are available. Automation can be a tremendous time-saver and deliver more accurate results. It makes successful testing more straightforward and faster.


Here are some frequently asked questions about integration testing.

What are the four types of integration testing?

Big bang, top-down, bottom-down, and hybrid testing are the four main types—the last three fall under incremental testing. The big bang approach is the only one that falls under non-incremental integration testing. 

What is the primary purpose of integration testing?

To test interfaces between two or more modules and expose any defects that may arise when these modules are integrated and have to interact with one another.

How to do integration testing?

The basic steps are:
1. Create an integration testing plan.
2. Create test data, test cases, and use cases.
3. Prepare the test environment.
4. Run test cases after unit integration.
5. Detect integration errors.
6. Apply required fixes to errors.
7. Retest functionality after fixing bugs.
8. Repeat the testing cycle until all errors are fixed.

How do you write test cases for integration testing?

Integration test cases have to cover all interface features. It's crucial for test teams to understand the application's structure and how the modules interact with one another. They should be familiar with any project peculiarities and able to analyze the results correctly.

What is integration testing in the software testing life cycle (STLC) model?

There are six main phases in the STLC model, they are:

1. Analyzing requirements.
2. Developing the test plan.
3. Developing test cases.
4. Setting up the test environment.
5. Executing tests.
6. Closing the test cycle.

Each stage has entry and exit requirements, activities, and deliverables. Test teams have to execute integration testing at the start of the STLC after concluding each unit test. They should make the resulting integration test report available for phase five as it is one of the entry requirements for this phase.


Integration testing is a crucial part of the software testing lifecycle. It is the second step of the testing process after unit testing. By running integration test cases on every software module, you will have a direct gateway to finding any defects in how modules interact.

When you apply programming logic to integration test plans and execute the integration testing properly, it can help save you from post-release updates and bug fixes. It can help eliminate common problems like API response generation, inadequate exception handling, and erroneous external hardware interfaces.

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Article written by Duncan Brigginshaw
Co-Founder and Technical Director

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