Yes. To be honest I found the mock test useful as there were some exercises, e.g. steep turns, that I had not done for a number of months prior to the test. In theory, the Skill Test only tests you on things you have done before, doing a mock ensures that you have done most things RECENTLY and should increase your confidence before taking the tet.
As with many testing situation, pre-test nerves have scuppered many a chance of passing. So take a mock, at least for the non-NAV part of the test, but make sure you have done at least one airborne diversion and are happy with the process.
Best wishes for the Skill Test.