Incremental testing is an approach used during the testing phase of integration tests. It uses a number of stubs and drivers to test each module independently. This helps identify any errors or defects in the modules
Following the completion of unit testing, integration testing is performed in order to detect the interfaces and interactions between different modules. As the integration process continues, a variety of methods and technologies are used, one of which is incremental testing. In this approach, developers sum up each module one by one using stubs or drivers.
As a developer, once you complete unit testing, you will need to perform integration testing. This process verifies how interfaces perform and how different modules interact. When you integrate, developers make use of tons of techniques. One among them is known as the incremental approach.
When you perform incremental integration testing, you can integrate different modules with the help of drivers or stubs to fix the bugs.
Incremental testing has its own set of advantages when you want to test a variety of elements. This is why you need incremental testing:
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When a tester has to perform integration testing, he will find incremental testing as a boon. The major reason for this to happen is that both integration testing and incremental testing are the same way. When we perform incremental testing, we verify the system's elements separately. This way, the testing specialist can achieve faster and better results to support the developers.
Do you want to learn more about exploratory testing? Here is a video:
Before we discuss in detail about incremental testing, we need to know about stubs and drivers. They are nothing but the dummy or pseudo code we use in component testing or integration testing. We use them when one or more than one modules are under development, but you need to test another module.
We use stubs in the top-down test strategy. We can also address them as “called programs.” Through stubs, you can simulate different interfaces between the underdeveloped lower lever module.
On the other hand, we use drivers in the bottom-up testing approach. They are also called “calling programs.” Drivers can simulate the interface between different top-level modules which might not be available or are still under development.
Many of us might have a question needing an answer:
The best thing to note is that developers would have to sit idle until every module is developed. This would also make it challenging to analyze the root cause of the defect. To prevent that from happening, we make use of stubs and drivers.
Let’s take a look at different Incremental Testing methodologies:
As evident from the name, you can perform code-based testing from top to bottom. It happens right from the central module and ends at the sub-module. This method first tests the modules from the top application layer. Generally, we involve the structural flow of the application under testing when we use this approach. We can substitute unavailable or underdeveloped components or modules with stubs. This testing type, where you can integrate and test every module at the layer-side first, is called “breadth-first”.
For top-down Incremental Integration testing approach, these will be the delivered test cases:
And so on other test cases are derived.
The next category would be “depth-first”.
You can derive the following test cases for “depth-first”:
You can similarly derive other test cases.
With top-down methodology, you get to access early architecture defects easily. This can teach you how an application would work in its early stages. Through this, you can easily identify any design defects. You can also test the main control points as early as possible.
Through this method, you can test the significant modules later in the cycle. It’s quite hard to write different test environment conditions. You cannot call a stub a perfect implementation of modules related to each other. It would simulate only the data flow happening between two modules.
Through this approach, you can understand that testing would take place from bottom to top. You can integrate and test the modules from the bottom layer first, and after that, you can sequentially integrate other modules as you keep moving up. You can replace underdeveloped or unavailable modules with drivers.
Here is an example to help you understand better:
Modules of healthy food, fruits, vegetables, citrus fruits, oranges, and lemons are under development. Hence we can substitute them with related Drivers:
For the bottom-up Incremental Integration testing approach, the following test cases will be derived:
We can use this method for applications with a bottom-up design model. You can easily create different test conditions using a bottom-up approach. When you start testing right from the testing hierarchy’s bottom level, it means you can test critical functionality or modules quite early. This way, you can easily identify any errors and bugs. You can also detect any defects in the interface early.
Sandwich testing approach is a hybrid method of both top-down and bottom-up methodologies. We use stubs and drivers to manage underdeveloped or incomplete modules.
Here is an example:
The following test cases can be derived with Sandwich Testing Strategy:
Whenever you carry out a big project with plenty of sub-projects, this method is beneficial. You can also run top-down and bottom-up testing methodologies parallely.
It’s not rocket science to perform incremental testing for any well-experienced tester. These pointers can help you out when you perform incremental testing:
Developers and testers can also harness LambdaTest’s HyperExecute - an end-to-end test orchestration cloud to run automated test suites at a blazing speed of up to 70% more than any other conventional cloud grids.
With incremental testing, you can quickly achieve the results you wish to accomplish from integrated tests. It’s always better to involve the right team to derive the best results. Integration testing, combined with incremental testing, provides developers and testers with the results they always aim for. The best development team, combined with the best test execution platform, can make this happen.
The two types of incremental integration testing are horizontal and vertical incremental testing.
When the relationship between different modules isn’t as obvious as it should be, we bring in big bang integration or non-incremental integration testing. With this testing, we create the data in a single module. We then combine it with different modules to test and check the data flow between them.
The two categories of incremental integration are Top-down incremental integration and Bottom-up incremental integration.
Shahzeb currently holds the position of Senior Product Marketing Manager at LambdaTest and brings a wealth of experience spanning over a decade in Quality Engineering, Security, and E-Learning domains. Over the course of his 3-year tenure at LambdaTest, he actively contributes to the review process of blogs, learning hubs, and product updates. With a Master's degree (M.Tech) in Computer Science and a seasoned expert in the technology domain, he possesses extensive knowledge spanning diverse areas of web development and software testing, including automation testing, DevOps, continuous testing, and beyond.