Test Cases Base – Customer Requirement Or Development Requirements?

I recently met with a test team with an excellent performance record. For all the applications where it had given a green have a track record of zero major bug encounter post its launch and 100% customer satisfaction with timely sign off. Definitely the credit goes to this test lead and his team. It was a point of curiosity at my end to know what was their process and methodology to give such a tremendous performance. Their logic was very clear and crisp. The team lead had made a rule that during all customer requirements capturing by business analysis team – one QC member will be part of the team. Customer requirement finalization doc once signed by customer would be shared with testing team. The testing team, on getting customer requirements documents, would immediately start building test cases where on the other hand, requirements have reached to development team for preparing development plan, testing plan and release date. While the development team is busy with meeting with their timelines, test team members had a clear cut charter of brainstorming and finalization of test cases built on the basis of customer requirements purely.