MeshTest now compares selection between evaluated mesh and expected mesh. This way, we can test more operators
such as `faces_select_linked_flat`
Note: selection comparison intentionally does not happen in BKE_mesh_cmp() on C side but rather on Python side, because
selection is independent of mesh generation.
Reviewed By: calra, mont29
Differential Revision: https://developer.blender.org/D10279