Functional testing involves testing either an element of a product or the complete product. This testing is used to determine whether the product will work as planned.
More importantly functional testing can be used to determine whether a product will work when used by a typical customer.
The product can be logically broken down into various elements, that is its functions. Any product that is marketed today needs to undergo rigorous functional testing to ensure that it's functions work correctly.
That is they work according to the specifications highlighted at the requirements stage of developing the product.
Consider the alarm clock, this must be able to perform certain functions in order to be marketable. Functions such as:
display the time correctly
the alarm works as set
the date is correct
These are some of the functions of the alarm clock, without these functions working correctly it would be difficult to use the alarm clock.
This would therefore mean, the alarm clock would not be fit for the purpose it was designed for.
If the object under test is a car then for functional testing, some of the items listed below, will need testing, such as,
switches for turning on headlights,
seatbelts working in accordance with regulatory standards,
the steering wheel turning the wheels correctly,
the car reversing when reverse gear is engaged.
These are some important parts of the car's functional tests. These items all need to be tested thoroughly to ensure that the car's functions do work as they were designed and required to do so.
If the object under test is an airplane then for functional testing, some of the items listed below, will need testing, such as,
correct instrumentation readings,
emergency oxygen releasing mechanisms work,
external doors lock to leave airtight seals.
These are some important parts of the airplane's functional tests. These items all need to be tested thoroughly to ensure that the airplane's functions do work as they were designed and required to.