  We use $\Lambda$CDM cosmological hydrodynamical simulations to explore the
kinematics of gaseous discs in late-type dwarf galaxies. We create
high-resolution 21-cm 'observations' of simulated dwarfs produced in two
variations of the EAGLE galaxy formation model: one where supernova-driven gas
flows redistribute dark matter and form constant-density central 'cores', and
another where the central 'cusps' survive intact. We 'observe' each galaxy
along multiple sight lines and derive a rotation curve for each observation
using a conventional tilted-ring approach to model the gas kinematics. We find
that the modelling process introduces systematic discrepancies between the
recovered rotation curve and the actual circular velocity curve driven
primarily by (i) non-circular gas orbits within the discs; (ii) the finite
thickness of gaseous discs, which leads to overlap of different radii in
projection; and (iii) departures from dynamical equilibrium. Dwarfs with dark
matter cusps often appear to have a core, whilst the inverse error is less
common. These effects naturally reproduce an observed trend which other models
struggle to explain: late-type dwarfs with more steeply-rising rotation curves
appear to be dark matter-dominated in the inner regions, whereas the opposite
seems to hold in galaxies with core-like rotation curves. We conclude that if
similar effects affect the rotation curves of observed dwarfs, a late-type
dwarf population in which all galaxies have sizeable dark matter cores is most
likely incompatible with current measurements.
