  In non-central heavy-ion collisions unprecedented strong magnetic fields, of
the order of 10$^{18}$ Gauss, are expected to be produced. The interplay of
such fields with QCD anomalies in the Quark--Gluon Plasma (QGP) has been
predicted to lead to a number of interesting phenomena, such as the Chiral
Magnetic Effect (CME). While several experimental observations are partially
consistent with predictions of a CME signal, it is hard to distinguish them
unambiguously from a combination of more mundane phenomena present in the
anisotropic expansion of the QGP. This makes it imperative to establish that
the early-time magnetic field has observable consequences not related to the
anomalous QCD effects on final-state charged particles and to calibrate its
strength. We test a recent prediction of a pure electromagnetic effect, which
may arise in heavy-ion collisions. The varying magnetic field would induce a
current within the QGP, which is expected to leave a very peculiar imprint on
final-state particles: a contribution to directed flow which is asymmetric both
in charge and pseudorapidity. We report the measurement of the charge
dependence of directed flow with respect to the spectator plane for
unidentified charged particles in Pb--Pb collisions at $\sqrt{s_\text{NN}} =
5.02$ TeV.
