Development and Writing Test Cases

Have any of you had any experience with being in this situation? I'm currently working with a well known producer of "fizzy brown sugar water" amongst other fizzy drinks. I (along with the company I work for) are developing systems for use in producing these products. As well as developing the system, they want us to develop test cases to test the system, with no oversight from their end, they just want to see that the tests passed.

Is it just me, or does this sound a little crazy?

With previous clients, a BA on our side has worked with the client to develop the use cases and test cases.

How does this sort of stuff work for others?