Application development is an expensive and time-consuming process. Any errors and mistakes occurring at the time of final deployment can lead to very serious consequences. The coding, done by the developers according to the requirements, is based on rules that may be based on few assumptions. Being human, we may make mistakes in either collection of requirements, or making up the assumptions. If this is the work done by us, who can better understand it than us? Unit testing tests the code, and helps in ensuring that it works fine.

The developers develop an application. Their development is based on some assumption, and they may leave out a few blind spots as well. Development is followed by testing the developed component. It's high risk for the tests to be carried out by the same persons, as they may repeat the same mistakes. Ideally, someone else should do the check, assuming that they know what they are testing.

The following are the few major factors that makes the testing an unforgettable part of application development:

• It helps in early detection of defects and errors made during development
• It ensures least failure in application executions
• It helps in improving the consistency of an application
• It helps in ensuring better application quality
• It helps in improving security by checking authentication and authorization
• It helps in saving money and, more importantly, time

To ensure that the application matches the requirements, and the correctness of all its functionalities, each application undergoes rigorous testing before it is released. Unit testing, integration testing, system testing, and acceptance testing are the four major stages through which each application needs to pass.