IEC 61124:2023 gives a number of optimized test plans, the corresponding border lines and characteristics. In addition, the algorithms for designing test plans using a spreadsheet program are also given, together with guidance on how to choose test plans.
This document specifies procedures to test whether an observed value of

• failure rate,
• failure intensity,
• mean operating time to failure (MTTF),
• mean operating time between failures (MTBF),

conforms to a given requirement.
It is assumed, except where otherwise stated, that during the accumulated test time, the times to failure or the operating times between failures are independent and identically exponentially distributed. This assumption implies that the failure rate or failure intensity is assumed to be constant.