Achieving fast development of good-quality software products is as important as achieving pure functionality. Qualified software development provides client satisfaction, reduces post-deployment costs and certificates the products. In addition to increasing quality, clients expect to tailor the products according to their needs and therefore, product configurability becomes more and more critical. Hence, the software manufacturing is required to adapt this configurable development process correspondingly. Software product line is a paradigm that purposes faster development of qualified software products that belongs to a particular domain. This thesis concentrates on quality assurance in software product lines and provides novel model-based approaches which are full test sequence composition and incremental test sequence composition approaches that aim to reuse existent test artefacts. Full test sequence composition approach reuses the existing test models and the test sequences are composed from scratch each time a product variant's test sequences are generated. Incremental test sequence composition approach reuses both of the test models and the existing test sequences of product variants. Whenever a product variant's test sequences are generated, existing test sequences and features which are incrementing the existing product are composed. The proposed approaches and the classical test generation of ESGs are compared, the results show that the incremental test sequence composition is the best in terms of both test set size and test generation time, the full test sequence composition is better than the single model ESG test generation in terms of test suite size but not in terms of test generation time.