Difference between Top Down and Bottom Up Integration Testing

Top down integration testing can be done in a couple of ways that resemble the popular tree traversing techniques in data structures. Also, please note that the usage of stubs is only applicable to top down integration testing. Here, the central module is Module 1, which we will have to reach ultimately, and the smaller isolated modules are Module 2 and Module 3, and so on.

top-down testing

The top-down method allows the tester to write placeholders, known as stubs, for lower-level modules that haven’t been implemented yet. Since the tester knows the expected outcome of these lower-level modules, they can simply write a stub that spits out the desired output. Sandwich Testing is a strategy in which top level modules are tested with lower level modules at the same time lower modules are integrated with top modules and tested as a system.

What are the key steps in integration testing?

Effective software testing heavily on incremental integration testing. In this approach, testing begins with the integration of multiple modules that are logically related, followed by functionality tests. In theory, top-down testing should find critical

design errors earlier in the testing process than other

approaches. Also, in theory, top-down testing should

result in significantly improved quality of delivered


software because of the iterative nature of the tests.

Sandwich integration testing, also know as hybrid integration testing, is a method that combines the advantages of both top-down and bottom-up strategies. Sandwich testing involves testing high-level modules and working down, while simultaneously performing tests on low-level modules and working up. Meaning lower-level modules are tested & integrated first to execute certain software functions.

But, it may seem impossible because it is hard to imagine how you can test one “piece” if the other “pieces” that it uses have not yet been developed (and vice versa). Lastly, top down https://www.globalcloudteam.com/ testing is simpler in complexity & data intensity as compared to bottom up testing. We’ve covered everything you need to know about top down and bottom up testing in this article.

When tested individually in unit testing, it may not uncover any errors. However, when these modules are integrated things such as data flow, API calls, request flow, and much more happen in the back end. This technique follows the control flow or architectural structure to test it from top to bottom. Unit testing is performed on the top module alone, followed by integration of the lower modules. In this way, all the modules are integrated and tested simultaneously.

If you are building your scrappy MVP, then integration testing probably isn’t worth your time. If you’re pushing out V1 and intend to scale your product, then this form of quality assurance testing is likely worthwhile. Integration testing helps to identify and resolve any issues that may arise when components are combined, such as compatibility issues, performance problems, incorrect communication, or data corruption.

top-down testing

With BrowserStack’s real device cloud, you can access thousands of real mobile devices for manual and automated app testing. Each device is loaded with real OS to help you achieve the best possible testing results. It combines elements of both top-down and bottom-up integration testing. This integration test case verifies that the different components of the retail website, such as the shopping cart, payment gateway, and order management systems, are working together to process an order. In this section, we are going to discuss the difference between top-down and bottom-up integration testing; and see a brief introduction of them.

Although my experience plays an important role in making every article ‘my own piece of work,’ I believe writing is a never-ending learning process where I am still a student. Besides creating content, I try to read every book there ever existed and travel to places that are within reach (for now). Below are the different strategies, the way they are executed and their limitations as well advantages. Software Engineering defines variety of strategies to execute Integration testing, viz. For example, if the movefighter method has not been written yet, a stub such as the one below might be used temporarily – which moves any player to position 1. A ‘Stub’ takes place of such subordinate unit during the Unit Testing.

  • If the submodule is not ready for integration yet, temporary modules called STUB are used for simulating the real submodule.
  • Top down integration testing comes with the following benefits for your system.
  • But, it may seem impossible because it is hard to imagine how you can test one “piece” if the other “pieces” that it uses have not yet been developed (and vice versa).
  • Ensure exceptional user experience across all devices and browsers.

The following subsystems to be tested are those that “call” the subsystems tested previously. The test drivers are used to simulate the “top” layer components that have not yet been integrated. If you do have a product, then you should look into integration testing and how it can strengthen the integrity of your product.

top-down testing

This is because stubs can be written more quickly than the lower-level modules they are replacing. In some cases, lower-level modules may depend on external input or even components from other teams, so it will save time to replace them with stubs when testing top-level components. Integration testing is vital in today’s IT and software development landscapes, especially when requirements are dynamic and deadlines are tight. Even when each module of the application is unit-tested, some errors may still exist.

This guide by Harish Rajora covers one of the types of incremental testing called top down, where we move ahead, starting from the main module and ending with the smallest sub-modules. Big Bang integration testing is when all of the components are combined and tested at once. The Big Bang method may seem more time-friendly at first because all tests are performed at once. However, the method can be less effective in the long run since it only tests the system as a whole and doesn’t isolate specific components. The Big Bang method may therefore cause you to overlook potential errors, leading to more issues later. The main difference between unit testing and integration testing is that in unit testing, individual modules are tested.

We will talk about the difference between Top-down and Bottom-up Integration testing for you to understand both approaches in detail. Moreover, top-down testing goes from major to minor components, whereas bottom-up testing goes from small to significant modules. Integration testing is a crucial part of the software development industry. Especially since client requirements are extremely dynamic and deadlines are limited.

Apart from these best practices, there are multiple strategies related to integrating testing you must be aware of. But to achieve your desired testing results, you must follow the best practices for integration testing. Although all these types have their use cases and advantages, this blog focuses on Top-down and Bottom-up approaches and the differences between them. Top-down testing follows a sequential path of dealing with the top modules before moving on to later or sub-modules.

top-down testing

After successful authorization, they are redirected to a page listing different subscription plans. Here, we have concluded that the execution of top-down and bottom-up approaches is required to test the software or the application. The difference between Top-down and Bottom-up Integration testing is that the former moves downward, and the latter moves upward.