Check that the initial condition setup for ionizing equilibrium works correctly. GEAR-RT can set the initial ionization state of the gas to the (collisional) ionization equilibrium at startup. This test makes sure that this setup works as expected. To do this, we set up particles in with a very high range of different internal energies, and only run for 1 step. The correct ion mass fractions should already be set in the zeroth output. Compile swift with: --with-rt=GEAR_1 --with-rt-riemann-solver=GLF --with-hydro=gizmo-mfv --with-riemann-solver=hllc --with-stars=GEAR --with-feedback=none Additional notes: - careful if running with periodicity on. The high difference in internal energies across the box edge will induce a mass flux when running with meshless schemes, and the solution won't be exact at output_0000 any longer since the particles will be kicked before the output is written.