Collisions test. Evolution of the gas and dust velocities (from top to bottom) for tests B and C (left and right columns, respectively). The dot-dashed black line represents the analytical solution. The other lines compare the numerical solutions obtained with the EXP integrator (orange) with other integrators, namely the first-order implicit RK1 (blue), the second-order fully implicit RK2 (purple), the MDIRK method with $\gamma =1-1/\sqrt{2}$ (green), and the MDIRK method with $\gamma =1+1/\sqrt{2}$ (red).