Software Development Life Cycle refers to all the activities that are performed during software development including- requirement analysis, designing, implementation, testing, deployment and maintenance phases. In this tutorial, we will refer to one of the most widely used SLDC model - V model.
V model is also known as Verification and Validation model. In V model, the testing phase goes in parallel with the development phase. Thus, the testing phase starts right at the beginning of SDLC.
As we can see in the above diagram, the test activities start in parallel with the development activities e.g. during the requirement analysis phase, acceptance-test cases are prepared by the testing team; during system design phase, the system test case are prepared. Similarly, for each phase of development a corresponding QA activity is performed. Later, when the deliverable gets ready, the QA artifacts are used to conduct the testing. Along with that, each phase of development phase is verified before moving to the next phase.