A testcheck is the examination of a selection from a population to see if the selected items are accurate. If an auditor using testchecking discovers errors, then a larger sample size is examined. For example, an auditor could review four credit memos to see if they are properly authorized; if they are, then the same level of authorization is assumed to extend to all credit memos.
The testcheck concept allows an auditor to complete work in a more efficient manner. However, this method will not spot issues with transactions that were not selected.