- shouldReturn403WhenNotAuthenticated: verifies the endpoint requires
a valid JWT token (anyRequest().authenticated() enforcement)
- shouldMarkOrderAsPaidSuccessfully: calls POST with @WithMockUser,
verifies response includes id, status=paid, and amountPaid=49.00
- shouldReturn404WhenOrderNotFound: mocks service to throw
OrderNotFoundException, expects 404 response
- Test helper creates minimal Order entity with explicitly set id,
plate, status, and amountPaid for realistic response mapping