The process of testing the interface between two modules or two software units is referred as integration testing. It is a type of software testing in which various components such as hardware and software are combined to meet the wide variety of business requirements and expectations.

Performing the integration testing in the Agile era is an integral part because it gives the utmost ease to communicate and collaborate with the development and testing teams. Moreover, according to the research, 97% of the software testing companies use the agile methodologies for the distinct phases of the software testing life cycle because it allows the organizations to solve the complex issues of the projects quickly and make them more convenient for delivering the 100% value in everyday tasks.

Types of Integration Testing

Integration testing can be performed in four ways:

1. Big Bang Approach

2. Top-Down Approach

3. Bottom-Up Approach

4. Hybrid Integration Approach

1. Bing Bang Approach in Integration Testing

Big Bang is the first method of integration testing in which all the software modules/components are merged at once. Then the identity of these multiple functions is evaluated separately.

Example of Big Bang Approach in Integration Testing

Suppose there are two components, one is a reports module, and another is a transaction module. First of all, the organization performs testing on these sections individually and later combined into one framework to do the tests in a streamlined manner. Make sure the integration tests will never be marked as successful until all the levels are not completed.

Advantages of Big-Bang Testing

  • Big-Bang integration testing requires minimal planning strategies and is appropriate for small systems.
  • All the modules are entirely checked in the whole system, and there is no hassle of immediate repairs.

Few Drawbacks of Big-Bang Testing

  • The issues at the module interfaces are discovered at very late stages due to combining all parts in the framework.
  • Sometimes the identified bugs are difficult to separate.
  • It is challenging to cover all the test scenarios of integration without skipping any single module.
  • There is a high risk of losing certain critical defects in the manufacturing process.

2. Top-Down Integration Testing

The top-down integration testing is carried out by using stubs that are regarded as the dummy module, and that can be replaced temporarily. The second method of integration testing in the software test life cycle is preferred by the software testers to understand the behavior of low-level components, which are not incorporated yet. Furthermore, stubs, the replacement for the 'called' modules are used when there is a need for interaction of the software with an external system.

The chief purpose of using the top-down type of integration testing in STLC is to start the tests from top to bottom. Let's understand its example:

Example of Top-Down Approach in Integration Testing

Suppose there are three modules that are 1,2 and 3 and whereas there are six stubs like stub1, stub2, stub3, stub4, stub5, and stub6.



  • In the first phase, modules 1, 2, and 3 will be integrated by the integration testers, and the rest may be put on hold. After that, when stubs are included in the process, the order of the integration will become module 1, module 2; module 1, module 3; module 2, stub 1; module 2, stub 2; module 2 stub 3, module 3, stub 4; module 3, stub 5; module 3, stub 6;
  • It checks the compatibility between module 2 and stub 1, stub 2, stub 3. Similarly, evaluate the alignment between module 3 and stub 4, stub 5, and stub 6.

Advantages of Top-Down Testing

  • With a top-down approach, the major designing bugs can be easily found and fixed on the priority.
  • The crucial decisions or verification is made in the more initial test stages.
  • The very minimal amount of time will be required to write the stubs. It provides consistency, and the first scope method allows someone to deploy the complete functionality of the software.

Few Drawbacks of Top-Down Integration Testing

  • The core feature of the program is checked at the end of the process.
  • The checking of subsystems can be insufficient at the lower stage.
  • There are two many stubs required to do the top-down tests.

Also Read: The Rising & Flourishing Software Testing Market

3. Bottom-Up Integration Testing

Bottom-up is the third method in which testing is taking place from bottom to upside. The testing strategy provides to check the lower level of modules with higher modules before checking all the features of the program. The method is also known as inductive logic or inductive reasoning. The components of the lower hierarchy are reviewed on an individual basis, and further, the attached or relied parts are tested.

Advantages of Bottom-Up Testing

  • The bottom-up design methodology is valuable for testing the applications.
  • It is so easy to create and meet the test conditions with bottom-up integration.
  • It allows us to observe the test results faster.
  • When low-level frameworks with their associated functions are used by other modules, this method is regarded as very useful to evaluate them first and makes it convenient to accomplish the accurate integration of the following subsystems.
  • The critical modules are built and tested on the first because the testing starts from the bottom of the hierarchy. That means if any bugs occur in the forms of modules, they are easily discovered in the earlier processes.

Few Drawbacks of Bottom-Up Integration Testing

  • Test engineers are unable to observe the functions of the system level, mainly which belong to the temporarily integrated system. It is hard to detect the machine level functions if the high-level test driver is taken into operation.
  • As an entity, the program doesn't exist if the last module is added.
  • The components which are replaced by the drivers are a bit more complicated than stubs.

4. Hybrid Integration Testing

Hybrid integration testing is also called Sandwich Integration testing that allows the organization to perform the tests with the combination of both top-down and bottom-up approaches. The integration software testing combines the standalone modules and then tests them in a single entity. During this stage, it lets the interface exchange the information among all of the modules. The name 'hybrid' exhibits that it requires both the integration techniques to get the project done.

Features of Hybrid Integration Testing in Software Testing Life Cycle

  • It is described in terms of three layers - the main target layer, a layer that is above the target layer, and a layer that is below the target layer.
  • The main focus of the testing is given to the middle level of the target layer and select the system based on the code structure and characteristics.
  • If the goal is to deliver the simple operating system in the earlier stages and to finish up the working versions of the application ASAP, then the hybrid integration can be rolled out.

Difference Between Stubs & Drivers?

Both are the dummy components and are created by test engineers for test purposes.


  • Stubs are mentioned as "called programs" and are desirable in the top-bottom methodology of the integration testing.
  • Stubs can be used for only low-level modules.
  • It is close to the elements, which are under examination and in a simple form.


  • Drivers are known as "calling programs" and are necessary to include in the bottom-up approach of the integration testing.
  • It represents higher levels of modules.
  • It is utilized when the module is not ready for the test and marked as more complex than stubs.

Why There is a Need to Choose Integration Testing in Business

The test cases of integration testing are very different than that of other phases of the software test life cycles. It permits us to perform the integration testing in the Agile era and focus mainly on the interfaces, data flow, and information exchange between the modules. It enables us to write the negative cases, unit test cases, and the most simple cases  at the early stage, and the execution is performed on every build-out.

  • The use cases can be created in real-time.
  • Ensures faster development and budget-friendly.
  • Easy to track and high code coverage.
  • Bugs can be captured faster and fixed due to the earlier stage of software development with top-down and bottom-up approach integration testing.
  • End-to-end testing is possible and can find a typical level of everyday issues in a system—for example - broken database, cache configuration.

Popular Tools used in Integration Testing

  • Validata.
  • Protractor.
  • Rational Integration Tester.
  • FitNesse.
  • Citrus Integration Testing.

The Bottom Line

Software integration testing can improve the test gaps and gives all-time assistance to cover quality tests. It is the best way to ensure that all the modules of the software will individually check to speed up the application functions and give a delightful user experience. The test accuracy and secure fault detection capabilities bring confidence in software integration testers and much allow them to ensure the quality to the business owners for their projects.

Is your system/ online application full of errors? Then, why are you sitting idle? Come and tell your unique business requirement to Bugraptors, the #1 software testing company in India & globally offer you the world-class service of the integration testing at the reasonable prices.


Kanika Vatsyayan

Kanika Vatsyayan is Vice-President – Delivery and Operations at BugRaptors who oversees all the quality control and assurance strategies for client engagements. She loves to share her knowledge with others through blogging. Being a voracious blogger, she published countless informative blogs to educate audience about automation and manual testing.


Add a comment

BugRaptors is one of the best software testing companies headquartered in India and the US, which is committed to catering to the diverse QA needs of any business. We are one of the fastest-growing QA companies; striving to deliver technology-oriented QA services, worldwide. BugRaptors is a team of 200+ ISTQB-certified testers, along with ISO 9001:2018 and ISO 27001 certifications.

USA Flag

Corporate Office - USA

5858 Horton Street, Suite 101, Emeryville, CA 94608, United States

Phone Icon +1 (510) 371-9104
USA Flag

Test Labs - India

2nd Floor, C-136, Industrial Area, Phase - 8, Mohali -160071, Punjab, India

Phone Icon +91 77173-00289
USA Flag

Corporate Office - India

52, First Floor, Sec-71, Mohali, PB 160071,India

USA Flag

United Kingdom

97 Hackney Rd London E2 8ET

USA Flag


Suite 4004, 11 Hassal St Parramatta NSW 2150

USA Flag


Meydan Grandstand, 6th floor, Meydan Road, Nad Al Sheba, Dubai, U.A.E