Integration Testing in 2024: Importance, Types & Challenges

Software testing is an essential quality assurance (QA) component. Detecting errors before releasing software and ensuring the stability of APIs and web services during the testing stage is seven times cheaper than the production stage. ¹ Integration testing is a phase in software testing that developers should not skip. This article looks at the types of integration testing, its importance, and its challenges.

What is integration testing?

Integration testing is a phase in software testing where software modules are combined into a group and tested together. The purpose of integration testing is to assess the compliance of a system by checking the software modules’ compatibility and interoperability. Integration testing reveals defects during the interaction between software modules when they are integrated.

Integration testing is the second level of the software testing process; it is situated before system testing and after unit testing. See Figure 1 below to see the four levels of the software testing process and how integration testing is situated among them.  

Figure 1: Levels of Software Testing

Sponsored

Integration testing is used frequently in API testing to ensure the stability of APIs. TESTIFI offers PULSE, an API test automation tool. It uses different tests such as integration, unit, end-to-end, functional, and UI/UX tests. PULSE can reduce cycle time and cost by 50% and improve documentation. Industry leaders such as BMW and Amazon use TESTIFI services.

Top 5 benefits of integration testing 

For software to work consistently, all software modules have to integrate and work together. With integration tests, the following five issues can be eliminated:

1. Each module is designed individually by a software developer. Because of the uniqueness of each module, incompatibility between them can occur and cause errors in a system. For modules to work together, they must work in unity. Integration testing ensures that this is the case.    
2. During and after module developments, clients may request a change of requirements. Unit tests for such new requirements can be inadequate because while unit testing is a faster method, it only tests parts of the application. Integration testing will be the better option.  
3. As the second step in the software testing level, integration testing brings a better understanding of a system. Depending on the result of the integration test, the tester can carry on system tests in a more composed way.
4. Software modules interact with APIs in many instances. Integration testing ensures that data transferred via modules to APIs are correct. 
5. System-level issues such as broken database schema and cache integration errors can be identified with integration testing. 

What are the types of integration testing?

There are initially two types of integration testing:

• Incremental 
• Non-incremental (big-bang approach). 

However, Incremental testing is further divided into three additional approaches: 

• Top Down
• Bottom Up
• Sandwich Approach (A combination of Top Down and Bottom up integration testing) 

See Figure 2 for a complete visualization for types of integration testing.

Figure 2: Types of Integration Testing

The use of stubs and drivers in integration testing

Before explaining each integration testing approach, it is important to define the two dummy programs of integration testing: stubs and drivers. These applications serve as stand-ins for the testing’s missing models. Drivers and stubs can service aspects that a module can supply by mimicking features and functions. This shortens unnecessary testing delays and speeds up the testing procedure. See Figure 3 for application of stubs and drivers

• Stubs are used in Top-Down integration testing.
• Drivers are used in Bottom-Up integration testing.

Figure 3: Stubs and Drivers

Source: Edureka. ²

Incremental integration testing

In the incremental testing method, testing is carried out by integrating two or more logically connected modules, and the application’s optimal operation is then tested. Once this process is complete, other related modules are incrementally integrated, and the process is repeated until all logically connected modules have been successfully integrated and tested. This process can be implemented with either Bottom Up or Top Down approach.

Top-Down integration testing

In the Top-Down approach, testing is carried out using a top-down technique, starting with the top-level module and working your way down. In order to verify the functionality of the finished software, each module is individually tested before being combined. In Figure 4 below, you can see a representation of the approach:

Figure 4: Top Down Approach

In Top-Down integration testing:

• Since testers start from top to bottom, the essential modules are checked first. In this way, more critical errors can be found earlier in this approach.
• Stubs are used extensively. It can be costly.
• While modules in higher levels are tested thoroughly, modules in lower levels can be neglected.

Bottom-Up integration testing

Bottom-Up integration testing is the opposite of Top-Down integration testing: Lower-level modules are tested first, then higher-level modules. Since bottom-up integration tests continue until all modules are tested, lower modules are often used to facilitate testing higher modules. In Bottom-up integration testing:

• Testers can test more efficiently if all modules of the developed level are ready. 
• It makes it simpler to provide testing progress as a percentage and aids in identifying the software development levels.
• Top-level software modules, which are often considered critical, are tested last. Thus error detection can be costly and time-consuming.

Sandwich Approach

Top-down and Bottom-up approaches are combined in the Sandwich Approach or Hybrid integration testing. In this testing strategy, top-level modules and lower modules are tested simultaneously. Hybrid integration testing makes use of both drivers and stubs. In the Sandwich Approach:

• All modules in a system are tested in a short period.
• This type of testing has the drawback that any conditions that are not mentioned in the integration tests will typically not be verified.
• It is the most complex process out of the three incremental testing methods.

Big-Bang Approach

Big-Bang Approach, or non-incremental testing, is the process where all modules in a system are coupled together and tested as one unit. Contrary to incremental testing, this approach is only viable when all combined components in a unit are ready and complete. This is why:

•  The Big Bang Approach is convenient for small systems.
•  There is no priority among software modules. Thus, critical modules are neglected during the process.

If you want to learn more about software testing and practices on quality assurance:

External Links

• 1. Celerity. The True Cost of a Software Bug: Part One. https://www.celerity.com/insights/the-true-cost-of-a-software-bug#:~:text=To%20illustrate%3A%20if%20a%20bug,the%20cost%20could%20be%20%2410%2C000.
• 2. Edureka https://www.edureka.co/blog/what-is-integration-testing-a-simple-guide-on-how-to-perform-integration-testing/