Operational Acceptance Testing or OAT as it's known for short, looks at how a product or service will operate under certain conditions.
Generally these conditions of operation include tests to determine how commonly used features used during day to day use, work as expected as well as those features which happen or are used during exceptional circumstances to normal operations.
So normal use on a washing machine for example, would involve using the one of the different wash cycles. Whilst an exceptional circumstance could involve testing electrical isolation. Whereby if the washing machine floods its surroundings, the expectation would be of the washing machine shutting down in a safe manner, by isolating the electrical power, so it does not become dangerous.
This isolation of the electrical circuits could be defined as an acceptable Operational Acceptance Test and actually tested, to ensure the washing machine does not electrocute the people who buy it.
Some organisations use the term Operational Readiness Testing or ORT for short, to describe Operational Acceptance Testing but both terms imply the same.
A few examples of how Operational Acceptance testing could be used are listed below.
Example 1. Check to see if the coolant levels on the car are low, does the car engine still remain operational? Or if the oil is low, does the engine still operate? These tests are testing various scenarios to see if the technology built into engine management systems can cope with changes.
Example 2. Checking to see if a car can brake, when one of the brake pads is worn out. This test could then be repeated with both brake pads worn out to check if the rear drum brakes can still stop the car.
Example 3. Checking to see if additional train safety measures work, so when a train goes through red signal, an alarm sounds. If the train carries on going through red signals, does automatic braking system come into action and slow the train down.
Example 4. Airplanes have dual controls, so if one control is disabled, a secondary control should still allow the control to work. So if the primary control for the landing gear is disabled, does the secondary control still have the power to bring the landing gear down?
Operational acceptance is checking whether the product or services features can operate as expected
Features can be those used in the day to day operation and those to ensure safe usage