diff --git a/test/dofs/test_hex8_face_dofs.jl b/test/dofs/test_hex8_face_dofs.jl
new file mode 100644
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+++ b/test/dofs/test_hex8_face_dofs.jl
@@ -0,0 +1,138 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+using Test
+using JuliaFEM
+using JuliaFEM: Hex8FacetMaps, build_hex8_facet_maps, FacetMassKernel, EdgeMassKernel
+using JuliaFEM: hex8_edge_length_physical, hex8_edge_orientation_sign
+using JuliaFEM: field_ndofs
+using JuliaFEM: DOFBasedCOOAssembler, DOFBasedCOOCache, assemble!, extract_system
+using LinearAlgebra
+
+@testset "build_hex8_facet_maps (single Hex8)" begin
+    mesh = create_unit_cube_mesh(Hex8)
+    maps = build_hex8_facet_maps(mesh)
+    @test maps.n_edges == 12
+    @test maps.n_faces == 6
+    @test size(maps.elem_face_gid) == (6, 1)
+    @test size(maps.elem_edge_orientation) == (12, 1)
+    @test size(maps.elem_face_orientation) == (6, 1)
+    @test all(o -> abs(o) == 1, maps.elem_face_orientation)
+    @test all(==(1), maps.elem_face_fraction)
+end
+
+@testset "hex8_edge_orientation_sign vs facet maps" begin
+    mesh = create_unit_cube_mesh(Hex8)
+    maps = build_hex8_facet_maps(mesh)
+    conn = mesh.connectivity[1]
+    for le in 1:12
+        @test hex8_edge_orientation_sign(conn, le) == maps.elem_edge_orientation[le, 1]
+    end
+end
+
+@testset "edge orientation on shared hex–hex edges (2×1×1 bar)" begin
+    mesh = create_structured_box_mesh(Hex8; xmin = 0.0, xmax = 2.0, nx = 2, ny = 1, nz = 1)
+    maps = build_hex8_facet_maps(mesh)
+    products = Int[]
+    for le1 in 1:12, le2 in 1:12
+        if maps.elem_edge_gid[le1, 1] == maps.elem_edge_gid[le2, 2]
+            push!(products, Int(maps.elem_edge_orientation[le1, 1] * maps.elem_edge_orientation[le2, 2]))
+        end
+    end
+    @test !isempty(products)
+    @test all(abs(p) == 1 for p in products)
+    # Some shared edges see opposite local directions (−1); others agree (+1)
+    # — both occur on this structured mesh.
+    @test any(==(-1), products)
+    @test any(==(1), products)
+end
+
+@testset "RT0FaceFlux / Nedelec1Edge dof counts (tags vs Float64)" begin
+    @test field_ndofs(DOF{Nedelec1Edge, Edge}, Hex8) == field_ndofs(DOF{Float64, Edge}, Hex8)
+    @test field_ndofs(DOF{RT0FaceFlux, Face}, Hex8) == field_ndofs(DOF{Float64, Face}, Hex8)
+end
+
+@testset "DOFHandler Face field + FacetMassKernel (unit cube)" begin
+    mesh = create_unit_cube_mesh(Hex8)
+    S = @DOFSet{flux::DOF{Float64, Face}}
+    elements, handler = create_elements!(mesh, Element{Hex8, Lagrange{1}, S})
+    @test handler.facet_maps isa Hex8FacetMaps
+    @test handler.total_dofs == 6
+
+    kernel = FacetMassKernel(mesh)
+    asm = DOFBasedCOOAssembler()
+    cache = DOFBasedCOOCache(elements, handler, mesh, kernel)
+    assemble!(cache, asm, kernel, mesh)
+    K, _ = extract_system(cache)
+    @test size(K) == (6, 6)
+
+    d = diag(Matrix(K))
+    @test all(d .> 0)
+    @test sum(d) ≈ 6.0 rtol = 1e-10
+    off = K - Diagonal(d)
+    @test norm(off) < 1e-12
+end
+
+@testset "FacetMassKernel two-element bar (shared interior face)" begin
+    mesh = create_structured_box_mesh(Hex8; xmin = 0.0, xmax = 2.0, nx = 2, ny = 1, nz = 1)
+    @test length(mesh.connectivity) == 2
+    S = @DOFSet{flux::DOF{Float64, Face}}
+    elements, handler = create_elements!(mesh, Element{Hex8, Lagrange{1}, S})
+    # Two hexes share one interior facet: 12 − 1 merged pair => 11 unique mesh faces.
+    @test handler.total_dofs == 11
+
+    kernel = FacetMassKernel(mesh)
+    asm = DOFBasedCOOAssembler()
+    cache = DOFBasedCOOCache(elements, handler, mesh, kernel)
+    assemble!(cache, asm, kernel, mesh)
+    K, _ = extract_system(cache)
+    d = diag(Matrix(K))
+    # Sum of face areas over all mesh facets (exterior SA is 10; interior shared quad adds 1).
+    @test sum(d) ≈ 11.0 rtol = 1e-10
+end
+
+@testset "hex8_edge_length_physical (unit Hex8)" begin
+    mesh = create_unit_cube_mesh(Hex8)
+    conn = mesh.connectivity[1]
+    X = Vec{3,Float64}[mesh.nodes[Int(conn[i])] for i in 1:8]
+    @test hex8_edge_length_physical(X, 1) ≈ 1.0
+    @test hex8_edge_length_physical(X, 9) ≈ 1.0
+end
+
+@testset "DOFHandler Edge field + EdgeMassKernel (unit cube)" begin
+    mesh = create_unit_cube_mesh(Hex8)
+    S = @DOFSet{circ::DOF{Float64, Edge}}
+    elements, handler = create_elements!(mesh, Element{Hex8, Lagrange{1}, S})
+    @test handler.facet_maps isa Hex8FacetMaps
+    @test handler.total_dofs == 12
+
+    kernel = EdgeMassKernel(mesh)
+    asm = DOFBasedCOOAssembler()
+    cache = DOFBasedCOOCache(elements, handler, mesh, kernel)
+    assemble!(cache, asm, kernel, mesh)
+    K, _ = extract_system(cache)
+    @test size(K) == (12, 12)
+
+    d = diag(Matrix(K))
+    @test all(d .> 0)
+    @test sum(d) ≈ 12.0 rtol = 1e-10
+    off = K - Diagonal(d)
+    @test norm(off) < 1e-12
+end
+
+@testset "EdgeMassKernel two-element bar (shared interior face)" begin
+    mesh = create_structured_box_mesh(Hex8; xmin = 0.0, xmax = 2.0, nx = 2, ny = 1, nz = 1)
+    S = @DOFSet{circ::DOF{Float64, Edge}}
+    elements, handler = create_elements!(mesh, Element{Hex8, Lagrange{1}, S})
+    # Two hexes share one interior quad facet ⇒ its four bounding edges merge pairwise:
+    # 24 − 4 = 20 unique mesh edges (see unique-edge counting on conforming meshes).
+    @test handler.total_dofs == 20
+
+    kernel = EdgeMassKernel(mesh)
+    asm = DOFBasedCOOAssembler()
+    cache = DOFBasedCOOCache(elements, handler, mesh, kernel)
+    assemble!(cache, asm, kernel, mesh)
+    K, _ = extract_system(cache)
+    d = diag(Matrix(K))
+    @test sum(d) ≈ 20.0 rtol = 1e-10
+end