Square Test 3D -------------- This is a 3D version of the "square test", consisting of a cube of high-density material in pressure equilibrium with a surrounding low-density region. These initial conditions are those used to produce the simulations presented by Sandnes et al. (2025), section 4.1. This test is used to investigate spurious surface tension-like effects from sharp discontinuities in a system that should be in static equilibrium. There are two initial condition generation files to test both an equal-spacing scenario, i.e., with different particle masses in the two regions, and an equal-mass scenario. The significant contributions from both smoothing error and discretisation error at the density discontinuity make the equal-mass test particularly challenging for SPH. Note that the default resolution_eta parameter is consistent with the use of a Wendland C2 kernel with ~100 neighbours. Some examples of configuration options with different hydro schemes: REMIX: `--with-hydro=remix --with-equation-of-state=planetary --with-kernel=wendland-C2` "Traditional" SPH (tSPH): `--with-hydro=planetary --with-equation-of-state=planetary --with-kernel=wendland-C2`