(An) optimal time for software testing under the user's requirement of failure-free demonstration before release

Abstract

Two approaches to the problem of optimal testing (or release) time for software are described. Most of the previous models are based on a restrictive assumption that the testing is terminated (i.e., the software is released) at the end of a prescribed period of testing time which is the decision variable to the problem. It implies the in-service reliability are determined prior to its testing. Under the assumption, a software is occasionally released with the reliability unassured, if failure occurrences are more frequent towards the end of testing. It may be inappropriate, if a software is developed by a second party on a contract basis. Because, in this case, the user usually requires a demonstration for justifying software release. To overcome the weaknesses of the on-going assumption of the previous models, two kinds of release policy which exclude the assumption are proposed. The proposed policies are different from the previous one in that they enable a software user to determine the time of release after observing τ periods of failure-free operation has been occurred. The study is divided into two parts according to the policy proposed. In the first part, the two stage testing with failure-free release policy is proposed and described: A software, after being tested by the developer for some time (in-house testing), is transferred to acceptance testing performed jointly with the user: During the acceptance testing, it is released when τ units of time specified by user is observed to be failure-free for the first time. The policy may be attractive to a user because he can extend the testing time by increasing τ. A software cost model for the policy is developed. An optimal in-house testing time and various quantities of interests, such as expected periods of acceptance testing, are derived based on the Jelinski-Moranda software reliability model. In the second part, a release policy based on the inter-failure time is proposed: A software is released duri...