Software quality assurance is being an emerging field of software engineering, advocating more stable solutions to real-world systems strongly. SQA is a formal procedure used to evaluate, document, and assure the quality of the work products at all phases of SDLC. Different factors may affect the quality of the system. The primary purpose of this research is to identify and understand various quality factors and their effect on software/system development. The relationships between these factors and SDLC phases are investigated, and another quality factor testability is proposed to the quality factor set of the system analysis & design. The expected results of the proposed solution have shown the importance of testability, specifically at system analysis & design phase of software/system development.