test(domains): add brick solver helpers for continuum regressions

test/domains/continuum/solve_brick_helpers.jl

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+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+"""
+Shared helpers for small `Hex8` brick regression tests (structured mesh,
+boundary DOF collection, interior load DOF).
+"""
+
+using JuliaFEM
+
+function brick_hex_mesh(nx::Int, ny::Int, nz::Int)
+    return create_structured_box_mesh(Hex8;
+        xmin = 0.0, xmax = 1.0, nx = nx,
+        ymin = 0.0, ymax = 1.0, ny = ny,
+        zmin = 0.0, zmax = 1.0, nz = nz,
+    )
+end
+
+function collect_vertex_dofs_on_nodeset(handler, mesh, set_sym::Symbol)
+    d = Int[]
+    for nid in get_nodes_in_set(mesh, set_sym)
+        append!(d, get_node_dofs(handler, Int(nid)))
+    end
+    sort!(unique!(d))
+    return d
+end
+
+function interior_uz_dof_index(handler, mesh; x_threshold::Float64 = 0.25)
+    for i in 1:length(mesh.nodes)
+        mesh.nodes[i][1] > x_threshold || continue
+        nd = get_node_dofs(handler, i)
+        return Int(nd[3])
+    end
+    error("no interior node for load (x_threshold = $x_threshold)")
+end
+
+"""First global DOF index for `field_idx` on `elem_id` (cell-centred fields)."""
+@inline function first_field_dof(handler, field_idx::Int, elem_id::Int = 1)
+    return handler.field_starts[field_idx][elem_id]
+end