The acceptance tests should be kept under version control, just as with unit tests and the system code.
Use the same methods as for unit tests and system code, but a different rule: consider no integration complete until 100% of the previously passing acceptance tests pass.
Organize the tests as you would any code.
The executable acceptance tests for a story are contained in one or more methods of a Java class.
If the customer can't work with executable tests, maintain corresponding spreadsheet files in which individual worksheets correspond to individual methods.
Keep the spreadsheets and executable tests in sync. If absolutely necessary, use programs to move the test case/data back and forth, but this will limit your ability to refactor the tests.
Try these ideas out yourself in the following exercise.