This feature is newly introduced on the platform which needs to be enabled from the back end by the Account manager at Mettl.
Once this feature is enabled for an account it becomes available for all the assessments of that account new/old.It also give you a choice to individually activated it for the desired assessment.
As this is an assessment level setting, so after getting it enabled for the accounts it can be enabled from the Assessment settings as shown below in the screen shots.
You need to click on the sample test link check box for enabling it for the assessment and can paste the complete link of an assessment inclusive of the schedule settings on that which you want the candidate to use for the sample test before starting the final test.
Once enabled, for Private schedules, the sample test link can be shared with the candidates via Test invitation Email:
For Open links,candidate is given an option to visit the Sample test link before launching the actual test.