Testing goes beyond just checking if the system modules function at all. The end-user experience will be defined by many more external factors than just the source code quality — such as production ecosystems, tools, databases, servers, and others. To validate all of them on both high- and low-level components, you might need to reconsider your approach and run tests to simulate your production environment. Big Bang Testing is an Integration testing approach in which all the components or modules are integrated together at once and then tested as a unit.

Priority should be given to integrating links over unit functions that have already been tested. In the top down integration testing approach, we first test the data records, then the data records integrated with Profile Page, and then all three. Top down integration testing is a type of incremental testing where we move from top to down and keep integrating modules as we move ahead. To understand the concept of top down integration testing, we can construct a small example with familiar components used in a web application.

Steps in Top Down Integration Testing

When https://1investing.in/ 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. In the Bottom-up approach, you will club together lower-level modules in clusters. Here, M3, M4, and M5 will make one cluster, and M7 will be another. Each of these two clusters will use control programs for Integration testing.

High risk of integration problems that are difficult to identify and diagnose. May be suitable for small systems or projects with a low degree of interdependence between components. During the execution of the test cases, do not choose test data. Determine the Integration Test Strategy that may be used first, and then create the test cases and data to go with it.

What is Bottom Up Testing?

The login page will call the Admin page after login but the Admin page is not ready yet. To overcome this situation developers write a dummy program which acts as Admin page. It uses test drivers to initiate and pass the required data to the sub-modules. The main module is designed first and then the submodules or subroutines are called from it. Identify errors in the interaction between system components at different levels. Integration testing checks if the interaction between system components is compliant with all requirements.

Once all the modules have been unit tested, integration testing is performed. Incremental testing is an integration testing approach where you can integrate the software module by module - one by one incrementally. This is a better approach than the big bang because it focuses on each module and smaller combinations.

As the name suggests, hybrid or mixed Integration testing combines Top-down and Bottom-up to achieve the advantages of both types. Top-down testing follows a sequential path of dealing with the top modules before moving on to later or sub-modules. Once Unit testing is over and you integrate separate modules to form a complete system, Integration testing comes into the picture. It follows certain specifications to examine the interaction and behavior of different modules as they come together to build a system. Study the Architecture design of the Application and identify the Critical Modules. Here do not concentrate much on the Login Page testing as it’s already been done in Unit Testing.

A driver is a piece of code which is emulating a calling function. Basically, we call the driver as the main function which calls other modules to form complete applications. If we want to test any module it is required that we should have a main program which will call the testing module.

Incremental testing - Core of Top down

You can choose the former if your top down and bottom up integration testing wishes to skip the coding part and move directly on to testing the application. As such, Integration testing follows two approaches—Top-down and Bottom-up—that offer an organized way of building a programming structure, all the while continuing the testing processes. We will talk about the difference between Top-down and Bottom-up Integration testing for you to understand both approaches in detail. At the time of module development, there are wide chances of change in requirements by the clients. These new requirements may not be unit tested and hence system integration Testing becomes necessary.

Integration testing is a crucial part of the software development industry. Especially since client requirements are extremely dynamic and deadlines are limited. Integration testing verifies if the different modules perform as they should when integrated together.

It is here when sub-modules are not available to integrate and test, stubs become useful. The stubs act as the placeholders and function the same way as the sub-module. In the earlier section discussing the Top-down testing approach, we mentioned two methods—Depth-first and Breadth-first. 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. Sometimes, modules at lower levels are tested inadequately . The process is repeated until each module is integrated and tested.

Advantages

While working on integration, sometimes we face a situation where some of the functionalities are still under development. So the functionalities which are under development will be replaced with some dummy programs. It is sub divided into Big Bang Approach, Top Down Approach, Bottom Up Approach and Sandwich or Hybrid Integration Approach . This process is carried out by using dummy programs called Stubs and Drivers.

The difference between Top-down and Bottom-up Integration testing is that the former moves downward, and the latter moves upward. Top-down focuses on designing and testing the top module before merging it with sub-modules. Bottom-up, on the other hand, combines the sub-modules to test them and moves upward thereafter. If the system consists of a greater number of sub-modules, this approach becomes time-consuming and complex. Incremental testing is when a minimum of two logically related modules are connected for testing, and the same process continues as more modules add to the system. There are several automation tools available to help you perform Integration testing.

If we could summarize their behaviors and work in a table for quick reference, we would get something as follows. And this sequence can be continued if there exists another level of modules. Top down integration testing comes with the following benefits for your system. 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. Module 6 may not be directly connected to Module 1, which we need to be cautious about as it may damage the complete testing flow.

Incremental testing is the most vital part of integration testing. The modules are added in ascending order one by one as per the customer's need. And the selected modules need to be related logically to each other. A piece of code that passes test cases to another piece of code.

The goal of this level of testing is to find flaws in the way various software components interact when they're combined. Move from the top-level module to the lower level.Move from the lower level module to the top level. Module-priority in development.The main module is developed before the submodules.Submodules are given preference in the development over the main module. When the likelihood of defects on the top modules is higher.When the likelihood of defects on the lower modules are higher. Stubs are used to perform top down testing.Drivers are used to performing bottom up testing. The difficulty level in learning and executionTop down testing is found to be simpler than its counterpart.Bottom up is a bit complex and may take a little more time to learn and perfect.

• For large applications, big bang integration testing can compromise the quality of an application by overlooking finer aspects.
• At different companies, different roles may be responsible for writing and running the integration tests.
• All high-priority defects must be repaired and closed before technical documentation and release notes are submitted.

Top down integration testing demands testing of each individual component along with integrated combinations with stubs that help focus on a single element at once. This enhances the quality of testing and hence the quality of the product. As of stub, this code can also be used when the upper-level module is either developed or not. However, please note that the usage of drivers is only applicable for bottom up testing. Conventionally, one may find the usage of stubs only applicable when the module is still under development.

The process is repeated until all top-level modules have been tested. The next level of modules is generated when the lower level modules have been tested and merged. A stub is created by the tester when high-level modules are being tested and the other modules are not yet created.