Testing plays a vital role in the software development life cycle. 

There are several testing methods, types, and different levels of testing. Understand what component testing is, its importance, its different types, and how to perform it with an example. 

What is Component Testing?

A software application is a combination of multiple components or modules. Testing the individual component of any application is called component testing. In this testing, the functionality and usability of each component are validated separately without integrating it with other components, also called module testing.

Why is Component Testing necessary?

The aim of testing any software is to achieve quality and ensure customer expectations are met.

• Component testing is the way to identify the issues at the module level, so defects are captured at the early stage for each module and hence reduces the efforts of both developers and testers while testing the entire application. 
• This testing eliminates the errors at the initial stage and builds confidence at the component level. 
• As this testing comes before integration testing, it is useful for the team to identify the issues at the component and integration level individually before testing the entire application by QA. 

Types of Component Testing

The concept of component testing can be varied from project to project and organization to organization. It mainly depends on the project’s complexity, the software development methodology used, and the component’s dependency on other components. 

Based on the complexity of the application, it is derived mainly in two ways:

Component testing in small

Testing is performed on the individual components without any dependency on another component of the application, it is called component testing in small. This testing best fits smaller applications.

There is a web application of practice questions for multiple subjects for different grades for a  school. Each subject page is developed and tested individually without any dependency on the other subject pages.

Component testing in large

Component testing is to validate the individual components with the help of other components, which means when the input or output of one component is required for testing the other component, it is called component testing in large. 

If any component development is yet to be completed, but there is a dependency to test, then dummy code snippets are placed to proceed with testing, called STUB or DRIVER.

Drivers and Stubs

Let’s dive into the concept of the Drivers and Stubs

Stubs and Drivers will be used in both component testing and Integration testing. These are needed to increase the efficiency of testing.

DRIVER

• A dummy code for mocking the behavior of a missing component is required to invoke the testing of the lower-level component. 
• This means the driver acts as a called function to the lower-level module when the calling function is not available. 
• A driver is a higher-level module in the list.

STUB

• A dummy code for mocking the behavior of a missing component, which is required for testing the other higher-level component.
•  A stub is a lower-level module in the list, Stubs will accept the inputs from the high-level module and return the output.
• In simple terms, There is an application with components A, B, C, and D. 
• Component B is output from A and C input for D, which are not yet developed.
•  Still, A and D are ready for component testing, so in this case, a stub is created for replicating component B, and a Driver is created for replicating component D. 

When is Component testing performed?

In SDLC, during the development phase, developers will do unit testing on that component and release a build to the QA team for testing that particular component alone. The entry criteria for component testing is the unit test completion. Then testers will do rigorous testing and validate the functionality against the requirements and report if any bugs are identified. 

Component testing is performed before Integration testing and after unit testing.

• Assume you are working on a project which has website development. Once the website’s pages are developed, the development team will do a unit test and release the build for the testing team to test the components. 
• Then testing team will do a test on individual pages of the website and will provide the test results. 
• In this case, developing all the web pages is optional before allowing the tester to do the testing.

How is Component testing performed?

QA team will do the component testing once the development and unit testing of the component is completed. Test strategy is vital in this method; the QA team will proceed with testing based on the planned testing methodology.  

Irrespective of the testing model, everyday activities performed in component testing are as follows:

Component Testing Example

Assume while testing a banking domain application for XYZ bank. The website will be designed with different pages like Accounts, Cards, Insurance, Investments Offers..etc, based on the services provided by the bank. Login pages are designed based on user levels like personal and business access. So if all the pages are designed as multiple components there after the completion of each component, testing can be done.

Based on customer requirements application is developed for different users, and each page is an independent component, so we test them without the dependency on other components (CTIS). 

Assuming the login page is yet to develop, the concept of the driver is applied here to ensure the testing of the accounts page

Similarly,  if we have to test the fund transfer page the concept of Stubs is applied to the Addpayee page. 

Component Testing VS Unit Testing

Advantages and Limitations of Component Testing

Advantages

Limitations

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