Most responsible Enneagram teaching states two things about its use, and both are worth passing on. The first is that a type is intended to describe a habitual strategy rather than a fixed identity, and the system's own literature warns against using it to explain people away, to excuse behaviour or to type others without their participation; the whole point of the passion and virtue pairing is that the type is what one is meant to work with, not what one is. The second is that self-typing by questionnaire is unreliable, that people commonly mistype themselves, and that the schools recommend reading the full descriptions and reflecting over time instead. To those two should be added a third, from outside the system: because the nine-type structure is not empirically established, the Enneagram should not be used for hiring, selection, or any decision affecting another person's life.
The instrument most often used for self-typing is the Riso-Hudson Enneagram Type Indicator (RHETI), which first appeared in Riso and Hudson's 1995 book Discovering Your Personality Type and was revised into the widely used version 2.5 in 1999. It is the questionnaire the contested-use research on the system has most often examined, and the same research that finds the type descriptions relate to established personality measures as predicted also finds that factor analysis of the RHETI's items does not cleanly recover nine separate factors, one more reason the schools themselves recommend reading the full type descriptions rather than relying on a test score alone.
Sources The Enneagram: G. I. Gurdjieff's Esoteric SymbolCarole M. Cusack with The Enneagram: A systematic review of the literature and directions for future researchJoshua N. Hook, Todd W. Hall, Don E. Davis, Daryl R. Van Tongeren and Mackenzie Conner