The higher level modules are the main modules and the lower level modules are the submodules. The top-down integration testing approach is simple and not data-intensive; on the other hand, the bottom-up integration testing approach is complex and data-intensive. The purpose of executing top-down integration testing is to detect the significant design flaws and fix them early because required modules are tested first. When each component or module works independently of an application, we need to check the dependent modules’ data flow, known as integration testing. To examine the risk in top-down testing approach the effect of the internal operational defects are combined.

In simple words, we can say that when there is a strong relationship between the dependent modules, we will perform the incremental integration testing. Both types have their advantages and disadvantages to help you decide which approach will best serve your needs. You can choose the former if your team wishes to skip the coding part and move directly on to testing the application. Requires more time than the Top-down approach as both lower and upper-level modules must be available for testing. The procedural programming languages such as Fortran, COBOL and C follows a top-down approach.

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All high-priority defects must be repaired and closed before technical documentation and release notes are submitted. Critical Modules are tested first; severe design faults may be discovered and corrected first. Critical Modules are tested first so that fewer chances of defects. Top-down approaches are backward-looking; on the other hand, the bottom-up approaches are forward-looking. In the top-down method, we will also make sure that the module we are adding is the child of the previous one, like Child C, is a child of Child B.

As the name suggests, hybrid or blended integration testing combines top-down and bottom-up to gain the benefits of both. Top-down testing follows a sequential path of addressing major modules before moving on to subsequent modules or submodules. Incremental testing is when at least two logically contiguous modules are connected for testing and the same process continues as more modules are added to the system. The Caltech Coding Bootcamp, ranked the Number One coding bootcamp by Career Karma, can turn you into a full-stack developer in six months!

Integration Testing is essential for ensuring that the software components work together seamlessly. Ensure that you have a proper Architecture / Technical Design document where interactions between each units are clearly defined. In fact, you will not be able to perform Integration Testing without this information.

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These modules are further decomposed until the resulting module is the fundamental program essentially be understood and can not be further decomposed. After achieving a certain level of modularity, the decomposition of modules is ceased. The top-down approach is the stepwise process of breaking of the large program module into simpler and smaller modules to organise and code program in an efficient way. The flow of control in this approach is always in the downward direction. The top-down approach is implemented in the “C” programming language by using functions.

In Top Down Integration Testing, testing takes place from top to bottom. High-level modules are tested first and then low-level modules and finally integrating the low-level modules to a high level to ensure the system is working as intended. Every software application contains multiple modules that converse with each other through an interface. Integrating these individual software modules and testing them together is known as Software Integration Testing. Since process-related communication flows top to bottom in top-down companies, it’s easy for individuals and groups to become siloed and eventually feel isolated. While following this upward testing direction, drivers are eliminated as main modules get developed completely.

On the other hand, in the bottom-up testing approach, the drivers simulate the main module, which means that the Driver works as a momentary replacement. At its foundation, Integration testing is the second level of testing right after Unit testing. All the system modules that are designed, developed, and tested during the Unit testing stage go through integration and further examination to check for compatibility issues. While Integration testing has multiple approaches that you can adopt as per your testing needs, two of the popular ones are Top-down and Bottom-up.

Developers create a dummy module say Stub to replace ‘Module B’. Same way if ‘Module B’ is dependent on ‘Module A’ but ‘Module A’ is not ready yet. While writing integration test cases, we don’t focus on functionality of the individual modules because individual modules should have been covered during Unit Testing. Here we have to focus mainly on the communication between the modules. As per our above assumption, we have to focus on “How Login Page is linked to the Inbox Page” and “How Inbox Page is linked to the Delete Mails module”.

Key Differences Between Top-Down and Bottom-Up Integration Testing

Integration testing verifies that all the parts communicate well and work together to achieve the purpose of the software. There are several automation tools available to help you perform integration tests. Some of the popular tools like Selenium,Pytest, Testsigma, and Protractor are all open source and offer a number of built-in options and use cases for testing purposes. The required test environment has been set up for integration testing. In the above example, the Login page is ready but not the Admin page. This time assume that the Admin page is ready to test but the Login page is not ready yet.

• Many teams go with the top-down approach because it eliminates confusion, reduces risk, and keeps initiatives organized across larger teams.
• We’ve covered everything you need to know about top down and bottom up testing in this article.
• Obtain the architectural team’s interface designs and write test cases to thoroughly check all of the interfaces.
• In the above example, the Login page is ready but not the Admin page.
• In the Bottom-up approach, you will club together lower-level modules in clusters.
• Structure/procedure-oriented programming languages implement top-down integration testing whereas bottom-up testing is implemented on the object-oriented languages.

Ultimately, the dummy difference between top down and bottom up integration testing would be completed with the proper program logic. However, developing the stub allows the programmer to call a method in the code being developed, even if the method does not yet have the desired behavior. A ‘Stub’ is a piece of software that works similar to a unit which is referenced by the Unit being tested, but it is much simpler that the actual unit.

Definition of Top-down Approach

As the name suggests, in this type of test, all the units or modules are grouped together and tested as a whole. Here we come to the bottom-up approach that provides a definitive picture of the difference between top-down and bottom-up integration testing. Existing test cases for the top-down approach would also work for regression tests to verify integration between modules.

Once all the lower-level modules are successfully tested and integrated, the next level of modules is formed. In Bottom Up Integration Testing, testing takes place from bottom to up. It is sub divided into Big Bang Approach, Top Down Approach, Bottom Up Approach and Sandwich or Hybrid Integration Approach .

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• The modules are added in ascending order one by one as per the customer’s need.
• This approach is advantageous if the significant bugs occur in the top modules.
• Integration testing comes after Unit testing and follows the communication between several software modules after their design, development, and integration.
• First of all, the top down approach utilizes stubs as a temporary replacement for lower modules whereas the bottom up approach uses drivers to simulate the higher-level modules.
• This integration of submodules and modules into the higher level module is repeatedly performed until the required complete algorithm is obtained.
• A ‘Driver’ is a piece of software that drives the Unit being tested.

Developers can use many different accepted software testing techniques in integration testing. Here’s a collection of some of the common techniques available from the field of software testing. These techniques are not to be confused with integration testing types, which we’ll cover the following section. The bottom-up style of management solves many of the problems that come with the top-down approach.

It is always a good idea to develop and test software in “pieces”. 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 . Lastly, top down testing is simpler in complexity & data intensity as compared to bottom up testing.

The challenges of the top-down management approach can be alleviated or even eliminated entirely if the people at the top of the process aren’t just good managers, but are leaders too. When approaching project objectives from the bottom up, a team will collaborate across all levels to determine what steps need to be taken to achieve overall goals. With all communication flowing from leaders to team members with little room for dialogue, the top-down approach allows fewer opportunities for creative collaboration. Less interdepartmental collaboration may also eliminate fresh perspectives and stifle innovation. The top-down management style is common, which means there’s less of a learning curve for new hires if they came from a company that uses this structure. As a team leader, you can help new team members adjust more quickly by incorporating some familiar elements of top-down methodology into your management style.

In Bigbang Approach, the entire project or system is completed, and the testing is done on the entire system. The team should create a test plan to determine the type of test and the desired results. Tests performed based on priority reveal major flaws you can fix before complete integration.

In many ways, it makes sense for project decisions to be made at the project level. However, projects are still impacted by higher-level factors like company goals, budgeting, forecasting, and metrics that aren’t always available at the team level. Processes designed from the bottom-up can suffer from blind spots that result from a lack of access to insights from upper management. In top-down processes, there are fewer opportunities for teams to give input or suggestions.