Additional test request check faces for box in box

[jon-proximafusion]

Can we have a test that is two cubes, one larger than the other, small cube inside large cube. boolean cut large cube with small cube

check the final gmsh object has 18 faces (duplicate surfaces at the interfaces)

6 faces on outside of big cube, 6 faces on inside of big cube and 6 faces on outside of small cube

small_box = cq.Workplane('XY').box(1,1,1)
big_box = cq.Workplane('XY').box(2,2,2).cut(small_box)

assembly = cq.Assembly()
assembly.add(small_box)
assembly.add(big_box)

then the test should be, does the gmsh model contain 18 faces

entities = gmsh.model.getentities(dim=2)

len(entities) == 18

[jmwright]

Completed via #7