See also the CoreDNS erratic plugin as an example:

• drop: drop 1 per AMOUNT of queries, the default is 2.
• truncate: truncate 1 per AMOUNT of queries, the default is 2.
• delay: delay 1 per AMOUNT of queries for DURATION, the default for AMOUNT is 2 and the default for DURATION is 100ms.

We've already got an equivalent delay test in the benchmarks, but could also try testing drop and truncate behavior in those tests as well.