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Tuesday, June 10, 2014

What is Reliability Testing in Software Testing?


What is Reliability Testing?

A system's reliability is a measure of stability and overall performance of a system collated during an extended period of time under various specific sets of test conditions.  This type of testing incorporates the results from non-functional testing such as stress testing, security testing, network testing, along with functional testing.  It is a combined metric to define a system's overall reliability.  A measure of reliability should be defined by business requirements in the form of service levels.  These requirements should then be used to measure test results and the overall reliability metric of a system under test.

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.

Parameters involved in Reliability Testing:
  • Dependent elements of reliability Testing:
  • Probability of failure-free operation
  • Length of time of failure-free operation
  • The environment in which it is executed


Key Parameters that are measured as part of reliability are given below:
  • MTTF: Mean Time to Failure
  • MTTR: Mean Time to Repair
  • MTBF: Mean Time between Failures (= MTTF + MTTR)


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



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