Ten 20 Years Old Usability Heuristics

Jakob Nielsen, one of the world's top experts in user interface design and application usability, was once already referred in Quick Testing Tips.

In today's tip I want to bring readers' attention to Usability Heuristics as ready-to-use test oracles. Please read entire list via the link provided, I put here just one as an example (per author's copyright requirements).
User control and freedom
Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.