In software development, functional testing is a form of software system testing that verifies whether software matches its design.

This article needs additional citations for verification. (December 2010)

Generally, functional testing is black-box meaning the internal program structure is ignored (unlike for white-box testing).^[1]

Functional testing can evaluate compliance to functional requirements.^[2]

Sometimes, functional testing is a quality assurance (QA) process.^[3]

Functional testing differs from acceptance testing. Functional testing verifies a program by checking it against design document(s) or specification(s), while acceptance testing validates a program by checking it against the published user or system requirements.^[4]

As a form of system testing, functional testing tests slices of functionality of the whole system. Despite similar naming, functional testing is not testing the code of a single function.

The concept of incorporating testing earlier in the delivery cycle is not restricted to functional testing.^[5]

Functional testing includes but is not limited to:^[1]

• Sanity testing, a.k.a. smoke testing
• Regression testing
• Usability testing

Functional testing typically involves six steps^{[citation needed]}

1. The identification of functions that the software is expected to perform
2. The creation of input data based on the function's specifications
3. The determination of output based on the function's specifications
4. The execution of the test case
5. The comparison of actual and expected outputs
6. To check whether the application works as per the customer need