Abstract: Estimating testability near the beginning in the software development process particularly at design stage is a criterion of key importance for software developers, designers, practitioners and quality controllers. As a matter of fact, researchers and practitioners highly advocated the need of an accurate and efficient measurement of software testability at design phase in development life cycle. There is a common understanding between academicians and industry professionals in incorporating testability in development life cycle in order to produce quality software. Unluckily, there is no standard guideline or methodology available to compute software testability. An endeavor has been put forth in this research paper to identify the testability key factors supporting in testability measurement especially at design phase of development life cycle. Study has identified the ‘Understandability’ and ‘Modifiability’ is the two major factors for measuring testability in design phase. Taking into account of their contribution in testability measurement a model has been developed to quantify object oriented design testability. After that the developed model has been validated with the help of experimental test and justified by statistical measures.

Keywords: Software Testing, Testability, Quality, Object Oriented Characteristics, Testability Factors.