  Let $X$ be an integral scheme of finite type over a complete DVR of mixed
characteristic. We provide a definition of a test ideal which agrees with the
multiplier ideal after inverting $p$, can be computed from a sufficiently large
alteration, agrees with previous mixed characteristic BCM test ideals after
localizing and completing at any point of residue characteristic $p$ (up to
small perturbation), and which satisfies the full suite of expected properties
of a multiplier or test ideal. This object is obtained via the $p$-adic
Riemann-Hilbert functor.
