  Self-testing results allow us to infer the underlying quantum mechanical
description of states and measurements from classical outputs produced by
non-communicating parties. The standard definition of self-testing does not
apply in situations when there are two or more inequivalent optimal strategies.
To address this, we introduce the notion of self-testing convex combinations of
reference strategies, which is a generalisation of self-testing to multiple
strategies. We show that the Glued Magic Square game [Quantum 4 (2020), p. 346]
self-tests a convex combination of two inequivalent strategies. As a corollary,
we obtain that the Glued Magic square game self-tests two EPR pairs thus
answering an open question from [Quantum 4 (2020), p. 346]. Our self-test is
robust and extends to natural generalisations of the Glued Magic Square game.

Quantum Physics