A key issue with Web Services (WS) is the verification and validation (V&V) of services to build trust between service providers and service users. This paper proposed a test-broker architecture so that all stakeholder within WS can contribute to improve the testing of the services. The test broker supports the submission, indexing, and querying of test artifacts such as test cases, defect reports and evaluations. It can also provide the services for the test generation, test coordination, and distributed testing services. The DCV&V (Decentralized, Collaborative, Verification and Validation) framework is proposed with a set of distributed and collaborated test brokers dedicated to different V&V tasks to enable scalable and flexible test collaborations. The paper explores the concept of design-by-contract and applies the principle to DCV&V. It identifies two categories of testing contracts including TSC (Testing Service Contracts) and TCC (Test Collaboration Contracts). It illustrates the application of TSC with contract-based test generation based on WS OWL-S specification. It elaborates TCC with the analysis of the test artifacts definitions.