  The IEEE 1788-2015 standard for interval arithmetic defines three accuracy
modes for the so-called set-based flavor: tightest, accurate and valid. This
work in progress focuses on the accurate mode.First, an introduction to
interval arithmetic and to the IEEE 1788-2015 standard is given, then the
accurate mode is defined. How can this accurate mode be tested, when a library
implementing interval arithmetic claims to provide this mode? The chosen
approach is unit testing, and the elaboration of testing pairs for this
approach is developed.A discussion closes this paper: how can the tester be
tested? And if we go to the roots of the subject, is the accurate mode really
relevant or should it be dropped off in the next version of the standard?
