What is Functional testing?
Functional Testing is a QA process and is a type of Black Box testing. Functional Testing is mainly used to verify whether a piece of software is providing the same output as required by client or end-user. Functional Testing implies testing the application against the business requirement. Functional testing always concentrate on customer requirements where as Non-functional testing is always concentrate on customer expectations.

Types of Functional Testing
Functional Testing has mainly two types:

1. Positive Functional Testing: This type of testing is done with valid inputs.

2. Negative Functional testing: This testing is done using a combination of invalid inputs.