From 9ee8157c54d70702833dadc2b736be51998b42bf Mon Sep 17 00:00:00 2001
From: Jukka Aho <ahojukka5@gmail.com>
Date: Mon, 15 Dec 2025 06:20:23 +0200
Subject: [PATCH] test(dofs): add DOF extraction test

New test file for DOF extraction functionality:
- Tests extract_element_dofs() function
- Tests extract_element_dofs_structured() function
- Single-field and multi-field test cases
- Type stability verification

Provides test coverage for DOF extraction from global solution vectors.
---
 src/dofs/test/test_extraction.jl | 101 +++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 src/dofs/test/test_extraction.jl

diff --git a/src/dofs/test/test_extraction.jl b/src/dofs/test/test_extraction.jl
new file mode 100644
index 0000000..6c847f8
--- /dev/null
+++ b/src/dofs/test/test_extraction.jl
@@ -0,0 +1,101 @@
+# Unit Tests for DOF Extraction
+# ===============================
+
+using Test
+using JuliaFEM
+using StaticArrays
+using Tensors
+
+@testset "DOF Extraction" begin
+    
+    @testset "VectorDOF{3} - 4 nodes (Tet4)" begin
+        u_global = rand(100)
+        dof_indices = (5, 6, 7, 20, 21, 22, 35, 36, 37, 50, 51, 52)
+        
+        result = extract_element_dofs(VectorDOF{3}, u_global, dof_indices)
+        
+        @test result isa SVector{4, Vec{3, Float64}}
+        @test result[1] == Vec{3}(u_global[5], u_global[6], u_global[7])
+        @test result[2] == Vec{3}(u_global[20], u_global[21], u_global[22])
+        @test result[3] == Vec{3}(u_global[35], u_global[36], u_global[37])
+        @test result[4] == Vec{3}(u_global[50], u_global[51], u_global[52])
+    end
+    
+    @testset "VectorDOF{2} - 3 nodes (Tri3)" begin
+        u_global = rand(50)
+        dof_indices = (10, 11, 20, 21, 30, 31)
+        
+        result = extract_element_dofs(VectorDOF{2}, u_global, dof_indices)
+        
+        @test result isa SVector{3, Vec{2, Float64}}
+        @test result[1] == Vec{2}(u_global[10], u_global[11])
+        @test result[2] == Vec{2}(u_global[20], u_global[21])
+        @test result[3] == Vec{2}(u_global[30], u_global[31])
+    end
+    
+    @testset "ScalarDOF - 4 nodes" begin
+        u_global = rand(100)
+        dof_indices = (10, 25, 40, 55)
+        
+        result = extract_element_dofs(ScalarDOF, u_global, dof_indices)
+        
+        @test result isa SVector{4, Float64}
+        @test result[1] == u_global[10]
+        @test result[2] == u_global[25]
+        @test result[3] == u_global[40]
+        @test result[4] == u_global[55]
+    end
+    
+    @testset "Type Stability" begin
+        u = rand(100)
+        inds = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
+        
+        # VectorDOF should infer concrete return type
+        @inferred extract_element_dofs(VectorDOF{3}, u, inds)
+        
+        # ScalarDOF should infer concrete return type
+        @inferred extract_element_dofs(ScalarDOF, u, (1, 2, 3, 4))
+    end
+    
+    @testset "Zero Allocation" begin
+        u = rand(100)
+        inds = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
+        
+        # Warm up
+        extract_element_dofs(VectorDOF{3}, u, inds)
+        
+        # Check GC pressure over many calls
+        GC.gc()
+        before = GC.gc_num()
+        
+        for i in 1:1000
+            extract_element_dofs(VectorDOF{3}, u, inds)
+        end
+        
+        after = GC.gc_num()
+        
+        # Should have negligible allocations
+        bytes_per_call = (after.allocd - before.allocd) / 1000
+        @test bytes_per_call < 10.0  # Less than 10 bytes per call
+    end
+    
+    @testset "Correctness vs Manual" begin
+        u = rand(100)
+        inds = (5, 6, 7, 20, 21, 22, 35, 36, 37, 50, 51, 52)
+        
+        # Manual extraction
+        manual = SVector(
+            Vec{3}((u[inds[1]], u[inds[2]], u[inds[3]])),
+            Vec{3}((u[inds[4]], u[inds[5]], u[inds[6]])),
+            Vec{3}((u[inds[7]], u[inds[8]], u[inds[9]])),
+            Vec{3}((u[inds[10]], u[inds[11]], u[inds[12]]))
+        )
+        
+        # @generated extraction
+        generated = extract_element_dofs(VectorDOF{3}, u, inds)
+        
+        @test generated ≈ manual
+        @test generated == manual  # Should be exactly equal
+    end
+    
+end