What is Component testing?: Component testing is a method where testing of each component in an application is done separately.  Suppose, in an application there are 5 components. Testing of each 5 components separately and efficiently is called as component testing.

• Component testing is also known as module and program testing. It finds the defects in the module and verifies the functioning of software.
• Component testing is done by the tester.
• Component testing may be done in isolation from rest of the system depending on the development life cycle model chosen for that particular application. In such case the missing software is replaced by Stubs and Drivers and simulate the interface between the software components in a simple manner.
• Let’s take an example to understand it in a better way. Suppose there is an application consisting of three modules say, module A, module B and module C. The developer has developed the module B and now wanted to test it. But in order to test the module B completely few of it’s functionalities are dependent on module A and few on module C. But the module A and module C has not been developed yet. In that case to test the module B completely we can replace the module A and module C by stub and drivers as required.
• Stub: A stub is called from the software component to be tested. As shown in the diagram below ‘Stub’ is called by ‘component A’.
• Driver: A driver calls the component to be tested. As shown in the diagram below ‘component B’ is called by the ‘Driver’.

Below is the diagram of the component testing:

As discussed in the previous article of the ‘Unit testing’ it is done by the developers where they do the testing of the individual functionality or procedure. After unit testing is executed, component testing comes into the picture. Component testing is done by the testers.

Component testing plays a very important role in finding the bugs. Before we start with the integration testing it’s always preferable to do the component testing in order to ensure that each component of an application is working effectively.

Integration testing is followed by the component testing.