Soak testing involves testing a system with a significant load extended over a significant period of time, to discover how the system behaves under sustained use.

For example, in http://www.answers.com/topic/software-testing - software testing , a system may behave exactly as expected when tested for 1 hour. However, when it is tested for 3 hours, problems such as http://www.answers.com/topic/memory-leak - memory leaks cause the system to fail or behave randomly.

Soak test are used primarily to check the reaction of a subject under test under possible simulated environment for given duration and for given threshold. Observations made during soak test used to improve the characteristics of the subject under test further.

In electronics, soak testing may involve testing a system up to or above its maximum ratings, for a long period. Some companies may soak test a product for a period of many months, while also applying external stresses such as elevated temperatures.