Performance testing is a rigorous usability evaluation of a working system under realistic conditions to identify usability problems and to compare measures such as success rate, task time and user satisfaction with requirements.
The goal of performance testing is not to find bugs, but to eliminate bottlenecks and establish a baseline for future regression testing.
To conduct performance testing is to engage in a carefully controlled process of measurement and analysis. Ideally, the software under test is already stable enough so that this process can proceed smoothly.
A clearly defined set of expectations is essential for meaningful performance testing.
For example, for a Web application, you need to know at least two things:
- expected load in terms of concurrent users or HTTP connections
- acceptable response time
Load testing:
Load testing is usually defined as the process of exercising the system under test by feeding it the largest tasks it can operate with. Load testing is sometimes called volume testing, or longevity/endurance testing
Examples of volume testing:
- testing a word processor by editing a very large document
- testing a printer by sending it a very large job
- testing a mail server with thousands of users mailboxes
Examples of longevity/endurance testing:
- testing a client-server application by running the client in a loop against the server over an extended period of time
Goals of load testing:
- expose bugs that do not surface in cursory testing, such as memory management bugs, memory leaks, buffer overflows, etc.
- ensure that the application meets the performance baseline established during performance testing. This is done by running regression tests against the application at a specified maximum load.
Although performance testing and load testing can seen similar, their goals are different. On one hand, performance testing uses load testing techniques and tools for measurement and benchmarking purposes and uses various load levels whereas load testing operates at a predefined load level, the highest load that the system can accept while still functioning properly.
Stress testing:
Stress testing is a form of testing that is used to determine the stability of a given system or entity. This is designed to test the software with abnormal situations. Stress testing attempts to find the limits at which the system will fail through abnormal quantity or frequency of inputs.
Stress testing tries to break the system under test by overwhelming its resources or by taking resources away from it (in which case it is sometimes called negative testing). The main purpose behind this madness is to make sure that the system fails and recovers gracefully -- this quality is known as recoverability.
Stress testing does not break the system but instead it allows observing how the system reacts to failure. Stress testing observes for the following.
- Does it save its state or does it crash suddenly?
- Does it just hang and freeze or does it fail gracefully?
- Is it able to recover from the last good state on restart? Etc.
