Functional Testing

Functional testing verifies that a system does what it is specified to do — that each feature behaves correctly according to its defined requirements.

What Functional Testing Covers

Functional testing asks a simple, direct question for every requirement: does this feature behave the way it's supposed to? It typically follows a black box approach, focused entirely on inputs and expected outputs rather than internal implementation.

• Does submitting a valid login redirect to the correct dashboard?
• Does an invalid discount code display the correct error message?
• Does adding an item to a cart correctly update the displayed total?

Common Mistakes

• Testing only positive scenarios (valid input, expected flow) and neglecting negative scenarios (invalid input, error handling).
• Writing functional tests based on assumptions rather than the actual documented requirements.
• Not updating functional test cases when requirements change, leaving outdated tests that no longer reflect intended behaviour.
• Confusing functional testing (does it do the right thing) with usability testing (is it pleasant and intuitive to use) — they're related but distinct.