 Software reliability is the probability that software will work properly in a specified environment and for a given amount of time. Using the following formula, the probability of failure is calculated by testing a sample of all available input states. Probability = Number of failing cases / Total number of cases under consideration

 Software reliability testing is a field of software testing that relates to testing a software's ability to function, given environmental conditions, for a particular amount of time. Software reliability testing helps discover many problems in the software design and functionality.

 To improve the performance of software product and software development process, a thorough assessment of reliability is required. Testing software reliability is important because it is of great use for software managers and practitioners.

 Software reliability is measured in terms of mean time between failures(MTBF).  MTBF consists of mean time to failure (MTTF) and mean time to repair(MTTR). MTTF is the difference of time between two consecutive failures and MTTR is the time required to fix the failure. Reliability for good software is a number between 0 and 1. Reliability increases when errors or bugs from the program are removed. For example, if MTBF = 1000 hours for average software, then the software should work for 1000 hours for continuous operations.

 The main objective of the reliability testing is to test software performance under given conditions without any type of corrective measure using known fixed procedures considering its specifications.

 The secondary objectives of reliability testing is:  To find perceptual structure of repeating failures.  To find the number of failures occurring in a specified amount of time.  To find the mean life of the software.  To discover the main cause of failure.  Checking the performance of different units of software after taking preventive actions.

 Feature test  Load test  Regression test

 Feature testing checks the features provided by the software and is conducted in the following steps:  Each operation in the software is executed once.  Interaction between the two operations is reduced and  Each operation is checked for its proper execution. The feature test is followed by the load test

 This test is conducted to check the performance of the software under maximum work load. Any software performs better up to some amount of workload, after which the response time of the software starts degrading. For example, a web site can be tested to see how many simultaneous users it can support without performance degradation. This testing mainly helps for Databases and Application servers. Load testing also requires software performance testing, which checks how well some software performs under workload.

 Regression testing is used to check if any new bugs have been introduced through previous bug fixes. Regression testing is conducted after every change or update in the software features. This testing is periodic, depending on the length and features of the software

 Reliability testing is more costly compared to other types of testing. Thus while doing reliability testing, proper management and planning is required. This plan includes testing process to be implemented, data about its environment, test schedule, test points etc.

 Some common problems that occur when designing test cases include:  Test cases can be designed simply by selecting only valid input values for each field in the software. When changes are made in a particular module, the previous values may not actually test the new features introduced after the older version of software.  There may be some critical runs in the software which are not handled by any existing test case. Therefore, it is necessary to ensure that all possible types of test cases are considered through careful test case selection