Performance testing is used to test the performance of software in a system. The performance testing can be done in every period of testing. Even in the element layer, the performance of a single module can also be evaluated by doing white-box testing. However, when the whole system is integrated, the actual performance of the system can be really tested.

Performance testing is often done with stress testing, and needs hardware and software testing equipments, which means, it is necessary to measure the use of resources in a demanding environment (for example, the processor cycle). The outward testing equipments can monitor the testing, when something happens (such as interruptions), it can record it. By testing the system, testers can find what reduces the efficiency and what causes the system bugs.

Stress testing is a kind of test which adds stress continuously to the system. By determining a system’s choke point or a failed performance point, the testing will enable you to know the maximum service level of the system. For example, you can measure when the system’s performance will decline or when it breaks down.

Performance test is a common used term when doing load test and force test alternately. Performance testing puts emphasis on the overall system. It has close relationship with the intensity, stress/load testing. Accordingly, stress and intensity testing should be done with performance testing.

The difference between stress testing and performance testing is their aim of the testing.

The aim of stress testing is to figure out the maximum load the system can support. The precondition is that the performance of the system can be tolerated. For example, it is usually agreed that the page should respond within 3 seconds. In a word, it tests the maximum load the system can bear on the condition that the performance can be tolerated.

Performance testing is for testing the response and the speed of the system and other performance indexes. Its precondition is that there is a certain load. For example, it will test the performance indexes when 100 users are online, and see if every user can operate normally. To sum up, it tests the performance of the system according to some indexes (such as the time of response) with different load (or with a certain load). If we say, some website performs badly, but to be exact, we should say, when how many people are online, the website performs badly.

In general, it is like a formula: overall performance=the load quantity*performance index. The overall performance is fixed, and stress testing is to test the biggest load when the performance indexes are the lowest, and performance test is to test the performance indexes when the load quantity is determined.