  A data-driven idea is presented to test if light nuclei and hypernuclei obey
the coalescence-inspired sum rule, i.e., to test if the flow of a light nucleus
or hypernucleus is the summed flow of each of its constituents. Here, the mass
difference and charge difference among the constituents of light nuclei and
hypernuclei are treated appropriately. The idea is applied to the available
data for $\sqrt{s_{NN}} = 3$ GeV fixed-target Au+Au collisions at the
Relativistic Heavy Ion Collider (RHIC), published by the STAR collaboration. It
is found that the sum rule for light nuclei is approximately valid near
mid-rapidity ($-0.3 < y < 0$), but there is a clear violation of the sum rule
at large rapidity ($y < -0.3$). The Jet AA Microscopic Transport Model (JAM),
with baryonic mean-field plus nucleon coalescence, generates a similar pattern
as obtained from the experimental data. In the present approach, the rapidity
dependence of directed flow of the hypernuclei $\mathrm{_{\Lambda}^{3}H}$ and
$\mathrm{_{\Lambda}^{4}H}$ is predicted in a model-independent way for
$\sqrt{s_{NN}} = 3$ GeV Au+Au collisions, which will be explored by ongoing and
future measurements from STAR.
