Off-the-shelf vs custom automated test systems/equipment
Anyone would want an out-of-the-box solution whenever possible. For some applications (like any testing meant to verify that a standard is being met, such as from SAE, IEEE, API, UL, and so on), the commonality is there to justify the creation of a ready-to-configure tester.
In many other cases, the product being tested is different enough from previous products and competing products, or does not have to meet an operational standard, that a custom (or, more commonly, a semi-custom) automated test system has to be developed for that specific UUT. When that’s the case, usually many of the hardware components (except maybe the fixture that attaches the UUT to the tester) are available off-the-shelf. There are also often pieces of software that can be re-used. These pieces of hardware and software then need to be integrated together into an automated test system.