  The verification of quantum devices is an important aspect of quantum
information, especially with the emergence of more advanced experimental
implementations of computation and secure communication. Within this, the
theory of device-independent robust self-testing via Bell tests has reached a
level of maturity now that many quantum states and measurements can be verified
without direct access to the quantum systems: interaction with the devices is
solely classical. However, the requirements for this robust level of
verification are daunting and require high levels of experimental accuracy. In
this paper we discuss the possibility of self-testing where we have direct
access to part of the quantum device. This motivates the study of self-testing
via EPR-steering, an intermediate form of entanglement verification between
full state tomography and a Bell test. Quantum non-locality implies
EPR-steering so results in the former can apply in the latter, but we ask what
advantages may be gleaned from the latter over the former given that one can do
partial state tomography. We show in the case of self-testing a maximally
entangled two-qubit state, or ebit, EPR-steering allows for simpler analysis
and better error tolerance than in the case of full device-independence. On the
other hand, this improvement is only a constant improvement and (up to
constants) is the best one can hope for. Finally, we indicate that the main
advantage in self-testing based on EPR-steering could be in the case of
self-testing multi-partite quantum states and measurements. For example, it may
be easier to establish a tensor product structure for a particular party's
Hilbert space even if we do not have access to their part of the global quantum
system.
