These are the index to the Dun & Dunn testaments - the period range is 1513-1901.
If a person wished to settle his or her affairs before death, they drew up a will, which set down their instructions as to the disposal of their possessions and named the executor whom they wished to administer the estate.
The executor had to be confirmed by the court and the document drawn up by the court for this purpose is known as a testament.
There are two types of testaments: the testament testamentar and testament dative.
The testament testamentar applied when the deceased died testate (leaving a will).
It comprised four parts: the introductory clause, an inventory of the deceased's possessions, the confirmation clause and a copy of the will, stating the wishes of the deceased regarding the disposal of the estate and naming the executor (usually a family member) he or she had chosen to undertake this task.
If a copy of the will was not included, reference was made to it having been recorded elsewhere, probably in the court's Registers of Deeds.
The testament dative was drawn up by the court if a person died intestate (without leaving a will), in order to appoint and confirm the executor on their behalf.
It comprised three parts: the introductory clause, an inventory of the deceased's possessions, and the confirmation clause. The testament dative might name a family member as executor, but if the deceased died in debt, a creditor might be appointed as executor instead. In such cases, the testament would include a list of the deceased's debts and would exist solely for the purpose of authorising the discharge of those debts.
The above is from www.scotlandspeople.gov.uk
Note: For some there are links to the wills - these are in pdf format - any problems with reading the early material let me know.