Test and inspection requirements originate in the design record (the drawing and associated standards and specifications). If there's a customer specification that addresses crimp integrity, it's expected that you'll have data to support compliance with it, rather than just your own assertions that everything's OK. The customer has already told you that data is expected, so if you're not sure about acceptable test methods you need to talk to the customer.
This is all a part of contract review--when a job is quoted, you need to review the specifications and make sure that you are capable of producing parts that meet specifications, and that you are capable of verifying that you've met them. In this instance, the need for pull-testing should have been established at the outset, so that associated costs could be accounted for in your quotation.