What are different aspects of stress testing?

Stress testing can be defined as a form of testing that is carried out to determine the stability and the stress handling capacity of a software system or module. Stress testing is all about testing the software system or application beyond the normal operational capacities. It is the testing of software system or application to its breaking or fatal point. This is done in order to observe the results.

Stress testing has a much broader meaning. What is basically understood by a stress test?
- It is referred to a test that mainly focuses upon the availability, error handling and robustness of a software system or application.
- In stress testing the software system or application is subjected heavy loads of tasks.
- It is not about considering the proper behavior under the normal operational conditions or user environment.

Typically the goal of stress testing is to test whether or not the software system or application crashes or fails in the case of catastrophic problems like unavailability of sufficient computing resources. These computational resources may include disk space or memory. It is also done to determine if the system crashes or fails under the situation of denial of service attacks and unusually high concurrency.

Stress testing, load testing, volume testing all seem like much similar kinds of testing.

A look at the following examples of stress testing will clear up the confusions regarding stress testing:


- Stress testing for web server:
A web server can be subjected to stress testing using bots, scripts and several denial of service tools to determine its performance and behavior during the peak data and tasks load.

- Stress testing can be studied in contrast with load testing.
Load testing is basically carried out to examine the entire testing environment and the huge database. It is also carried out to determine the response time of the software system or application whereas the stress testing exclusively focuses upon identifying the transactions and pushing them to a level at which a break occurs in the execution of the transaction software system.

Another point is that during the stress testing if the transactions are duly stressed, then the chance is that the database may not experience a huge data load. However if the transactions are not stressed, the data base may experience a heavy work load.

SOME IMPORTANT POINTS:
- Stress testing is another word for system stress testing.
- It can be defined as the loading of the concurrent users beyond and over the level that can be handled by the system.
- This leads to the breakage of the weakest link in the whole software system or application.
- While carrying out the stress testing the software engineers, developers or testers need to test the whole software system or application under the desired expected stress as well as under the accelerated stress.
- The goal here is to determine the working life of the software system.
- It is also aimed at determining the modes of failure for the software system or application.
- For the hardware counterpart of a complete system, the stress testing can be defined as the subjecting of the concerned hardware to the exaggerated levels of stress.
- This is basically done to determine the stability of the hardware system when used in a normal environment rather than a testing environment.
- Before modifying the CPU parameters during the processes of over clocking, over volting, under volting and under clocking, it is necessary to verify whether or not the new CPU parameters like frequency and core voltage are suitable for taking the heavy CPU loads.
- Stress testing for such parameters is usually carried out by executing a CPU intensive program for a prolonged significant period of time. It is observed if the system crashes or hangs.

What are different characteristics of stability testing?

Stability testing in the context of software testing and engineering as it itself
indicates, refers to the many attempts to determine if an application will crash.

- Stability testing seeks to find a fault, an error, a bug or a reason that can render the software system or the application as non working or which can make the application lame.
- The main objective of the stability testing is to determine if there are any grounds on the basis of which the software system or application should be kept void of certification and it also aims at finding some positive point on the basis of which the software system or the application can be granted the certification.

- For a software system or application to be certified, it should be in functional state and basically stable.
- This can only be done by applying specific and suitable criteria and tests for testing functionality and stability. This is nothing but the stability testing.

There are several criteria available for stability testing. Few have been discussed below in detail:

1. Pass or fail criteria
- Each primary function tested and then the results are recorded.
- Each and every individual function is operated or executed in a way that is apparently consistent with its objective or the purpose regardless of the degree of correctness of its result or output.
- The observations are recorded for analysis.
- It is certain that out of so many functions, at least one or two primary functions will prove incapable of operating in a way that it apparently consistent to their aim or purpose.

2. Functional ability of a software system or the application
- There is for sure some impairment in any software system.
- But that does not necessarily mean that the software system is not fit for normal use.
- Any software product or application is said to work abnormally in a way that it seriously impairs it for the normal usage.

3.Disruption criteria
- The software system or the application is observed to disrupt the normal functioning of the operating system.

4.Criteria of in-operability
- No primary function of the software system or application is observed to get obstructed and become inoperable and non functional during the course of the testing.
- There is at least one primary function of the software system or application is observed to get obstructed and become inoperable and non functional during the course of the testing.

5. The software system or the application is observed to crash, fail, loose data and hang.

Some Important Points:
- Stability can be defined as the ability of a software system or application to continue functioning in the case of over time and over its full range of functionalities without crashing, failing or hanging and loss of data.

- For a tester to know whether the software system is seriously unfit for normal and regular use, he /she is required to have a knowledge of how that software system or application works in a normal environment i.e., normal user and normal usage.

- In order to carry out the stability test, the tester requires knowing the types of data values which software system or application can effectively and efficiently process.

- To test for the instability of a software system, the tester needs to use his knowledge in order to give some challenging inputs to the system to fail the system.

What are the characteristics of testing and a good test?

Testing goal is to find errors. It should exhibit a set of characteristics that achieve the goal of finding the errors with minimum effort. The characteristics of software testing includes:
- How easily a software can be tested? i.e. test-ability
- How efficiently it can be tested? i.e. oper-ability
- What you see is what you test? i.e. observability
- How much we control the software so that testing can be automated and optimized? i.e. controllability
- Isolating problems and perform smarter retesting by controlling scope of testing i.e. decomposability.
- The program should be simple so that it can become easy to test i.e. simplicity.
- The fewer the changes, the fewer the disruptions to testing i.e. stability.
- The more information we have, the smarter we will test i.e. understandability.

A good test has the following characteristics:
- A good test has a high probability of finding an error.
- A good test is not redundant.
- A good test has the highest likelihood of uncovering a whole class of errors.
- A good test should be neither too simple nor too complex.

There are two ways to test an engineered product:
- Knowing the internal workings of product and tests can be conducted that can ensure that internal workings are performed according to specifications and all internal components are exercised properly.
- Knowing the output or the function for which the product is designed, tests are conducted to demonstrate each function is fully operational and checking the errors at the same time.

Categories of Heuristics of Software Testing

There is a set of characteristics that lead to a testable software.
- Operability: The better it works, more efficiently it can be tested.The system should have few bugs or no bugs that should block the execution of tests and the product should evolve in functional stages.

- Observability: What we see is what we test. It includes a distinct output should be generated for each input, the current and past system states and variables should be visible during testing, all factors affecting the output should be visible, incorrect output should be easily identified, source code should be easily accessible and internal errors should be automatically detected and reported.

- Controllability: The better we control the software, the more the testing process can be automated and optimized. Check that all outputs can be generated and code can be executed through some combination of input. Check that the software and hardware states can be controlled directly by the test engineer. Check that inputs and outputs formats are consistent and structured. Check that the test can be conveniently specified, automated and reproduced.

- Decomposability: By controlling the scope of testing, we can quickly isolate problems and perform effective and efficient testing. The software system should be built from independent modules which can be tested independently.

- Simplicity: The less there is to test, the more quickly we can test it. the points to consider in this regard are functional, structural and code simplicity.

- Stability: The fewer the changes, the fewer are the disruptions to testing. The changes to software should be infrequent, controlled and not invalidating existing tests. The software should be able to recover well from failures.

- Understandability: The more information we will have, the smarter we will test. The testers should be able to understand well the design, changes to the design and the dependencies between internal, external and shared components.

- Suitability: The more we know about the intended use of the software, the better we can organize our testing to find important bugs.

The above heuristics can be used by a software engineer to develop a software configuration which is convenient to test and verify.