Usability evaluation methods: which was first?

Nielsen and Molich introduced the heuristic evaluation method in 1990, and it was reviewed by Nielsen until 1995, when he exposed his 10 Heuristics for User Interface Design that currently still are a reference.

About user testing, the first reference that I could find is from Nielsen & Landauner (1993), but I'm not sure if it was invented at or before 1993.

Which one of these methods was invented first?