Component testing is fulfilled by programmers on the code written by them and with the support of development environment, such as a unit test structure or debugging tool.
Component Testing Example
For Example there are two web pages. In one of the web pages there are a many certain fields like username, address, mobile no. etc in which data has to be entered. In the other (second) web page also there are certain fields which carry forward the data from the first page. Testing the functionality of these individual pages is called Component Testing.
After component Testing
we always done the Integration Testing. While doing proper black box testing and white box testing by tester first of all Component Testing is done.
Before component Testing
Unit Testing is always done by the developers. While doing proper Unit Testing the Developers run each functions and method of the Component effectively.
Conclusion:
Component Testing is like "Unit Testing" with the difference that entire Stubs and Simulators are retrieved with the real objects. So here a Unit is a component, and integration of one or various such components is also a Component.