Validation phase - System Testing - Performance Testing - Capacity Planning - Stress Testing

Stress testing is another term that is used for performance testing. Though, load and stress testing are used synonymously for performance related efforts, their goal is different.
Unlike load testing, where testing is conducted for specified number of users, stress testing is conducted for the number of concurrent users beyond the specified limit. The objective is to identify the maximum number of users the system can handle before breaking down or degrading drastically. Since the aim is to put more stress on system. Think time of the user is ignored and the system is exposed to excess load.
The goals of stress testing are:
- It is the testing beyond the anticipated user base.
- It identifies the maximum load a system can handle.
- It checks whether the system degrades gracefully or crashes at a shot.

Stress testing also determines the behavior of the system as user base increases. Let us take an example of online shopping application to illustrate the objective of stress testing. It determines the maximum number of concurrent users an online system can service which can be beyond 1000 users. However there is a possibility that the maximum load that can be handled by the system may found to be same as anticipated limit.

The inference drawn from stress testing are:
- Whether the system is available or not?
- If yes, is the available system stable?
- If yes, is it moving towards unstable state?
- When is the system going to break down or degrade drastically?

Validation phase - System Testing - Performance Testing - Capacity Planning - Load testing

Load testing is much used industry term for the effort of performance testing. Here, load means the number of users or the traffic for the system. Load testing is defined as the testing to determine whether the system is capable of handling anticipated number of users or not.
In load testing, the virtual users are simulated to exhibit the real user behavior as much as possible. Even the user think time such as how users will take time to think before inputting data will also be emulated. It is carried out to justify whether the system is performing well for the specified limit of load.

Goals of Load Testing:
- Testing for anticipated user base.
- Validates whether the system is capable of handling load under specified limit.

The objective of load testing is to check whether the system can perform well for specified load. The system may be capable of accommodating more than say 1000 concurrent users. But, validating that is not under the scope of load testing. No attempt is made to determine how many more concurrent users the system is capable of servicing.
The inference drawn from load testing is :
- Whether the system is available?
- If yes, is the available system stable?