diff --git a/test/dofs/test_field_unification.jl b/test/dofs/test_field_unification.jl
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+++ b/test/dofs/test_field_unification.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
+
+"""
+Tests for field type unification.
+
+Tests that field types (Displacement{3}, Temperature, etc.) can be used directly
+in DOF specifications instead of quantity types (Vec{3}, Float64, etc.).
+"""
+
+using Test
+using JuliaFEM
+using Tensors
+
+@testset "Field Type Unification" begin
+    @testset "quantity_type() trait for field types" begin
+        # Test quantity_type trait on field types directly
+        @test quantity_type(Displacement{3}) == Vec{3}
+        @test quantity_type(Displacement{2}) == Vec{2}
+        @test quantity_type(Displacement{1}) == Vec{1}
+        @test quantity_type(Temperature) == Float64
+        @test quantity_type(DisplacementRotation{3}) == Vec{6}
+        @test quantity_type(DisplacementRotation{2}) == Vec{4}
+    end
+
+    @testset "quantity_type() with field types in tuples" begin
+        # Test quantity_type extraction from tuples with field types
+        S_u = @DOFSet{u::DOF{Displacement{3}, Vertex}}
+        @test quantity_type(fieldtype(S_u, :u)) == Vec{3}
+        
+        S_T = @DOFSet{T::DOF{Temperature, Vertex}}
+        @test quantity_type(fieldtype(S_T, :T)) == Float64
+        
+        S_ur = @DOFSet{u::DOF{DisplacementRotation{3}, Vertex}}
+        @test quantity_type(fieldtype(S_ur, :u)) == Vec{6}
+        
+        # Multi-field
+        S_Tu = @DOFSet{
+            T::DOF{Temperature, Vertex},
+            u::DOF{Displacement{3}, Vertex}
+        }
+        @test quantity_type(fieldtype(S_Tu, :T)) == Float64
+        @test quantity_type(fieldtype(S_Tu, :u)) == Vec{3}
+    end
+
+    @testset "DOF counting with field types" begin
+        # Single field: displacement
+        S_u = @DOFSet{u::DOF{Displacement{3}, Vertex}}
+        @test ndofs(Tetrahedron{4}, S_u) == 12  # 4 nodes × 3 components
+        
+        # Single field: temperature
+        S_T = @DOFSet{T::DOF{Temperature, Vertex}}
+        @test ndofs(Tetrahedron{4}, S_T) == 4  # 4 nodes × 1 component
+        
+        # Single field: displacement-rotation
+        S_ur = @DOFSet{u::DOF{DisplacementRotation{3}, Vertex}}
+        @test ndofs(Tetrahedron{4}, S_ur) == 24  # 4 nodes × 6 components
+        
+        # Multi-field: thermo-mechanical
+        S_Tu = @DOFSet{
+            T::DOF{Temperature, Vertex},
+            u::DOF{Displacement{3}, Vertex}
+        }
+        @test ndofs(Tetrahedron{4}, S_Tu) == 16  # 4 + 12
+        
+        # 2D displacement
+        S_u2d = @DOFSet{u::DOF{Displacement{2}, Vertex}}
+        @test ndofs(Triangle{3}, S_u2d) == 6  # 3 nodes × 2 components
+    end
+
+    @testset "Error handling for invalid formats" begin
+        # Test that non-field types in DOF produce errors
+        # Vec{3} is not a field type (should be Displacement{3})
+        S_invalid = @DOFSet{u::DOF{Vec{3}, Vertex}}
+        
+        # This should error because Vec{3} is not a field type (AbstractField)
+        @test_throws ErrorException quantity_type(fieldtype(S_invalid, :u))
+    end
+
+    @testset "field_type_for_dispatch with field types" begin
+        S = @DOFSet{
+            T::DOF{Temperature, Vertex},
+            u::DOF{Displacement{3}, Vertex}
+        }
+        
+        field_T = field_type_for_dispatch(S, :T)
+        @test field_T isa Temperature
+        
+        field_u = field_type_for_dispatch(S, :u)
+        @test field_u isa Displacement{3}
+    end
+
+    @testset "DOF manager with field types" begin
+        using JuliaFEM: DOFManager, _assign_element_dofs!
+        
+        mgr = DOFManager()
+        S = @DOFSet{u::DOF{Displacement{3}, Vertex}}
+        connectivity = (1, 2, 3, 4)  # 4-node tetrahedron
+        
+        dof_indices = _assign_element_dofs!(mgr, S, Tetrahedron{4}, connectivity)
+        
+        # Should return NamedTuple with :u field
+        @test haskey(dof_indices, :u)
+        @test length(dof_indices.u) == 12  # 4 nodes × 3 components
+    end
+
+    @testset "Element creation with field types" begin
+        S = @DOFSet{u::DOF{Displacement{3}, Vertex}}
+        # Element uses flat tuple of UInt64 for dof_indices
+        dof_indices = NTuple{12, UInt64}((1:12...,))
+        elem = Element{Tetrahedron{4}, Lagrange{1}, S}(UInt(1), dof_indices)
+        
+        @test elem isa Element{Tetrahedron{4}, Lagrange{1}, S}
+        @test length(elem.dof_indices) == 12
+    end
+end
+