Just look in Standards Document 7 and you will find the answer in 3.2.10 d:
Sufficient instrumentation to enable sustained operations in IMC which in any event shall include an airspeed indicator, altimeter, vertical speed indicator, attitude gyro, turn rate gyro and slip indicator. In aeroplanes approved for the IR test, a heading gyro and a second altimeter shall also be provided. This second altimeter shall be so positioned that it is clearly visible to both applicant and FE and adjustable by the applicant.
Which by my reading means that a DI is not mandatory for a CPL Skill Test.
Congratulations on passing!