test(domains): add heat topic runner

test/domains/heat/runtests.jl

@@ -0,0 +1,47 @@
+"""
+Test suite for the heat conduction domain.
+
+Heat is the second physics domain to ride the new microkernel contract
+(`reference_fields`, `qpoint_buffer_eltype`, `update_qpoint_buffer!`,
+`evaluate_entry`). The tests here are deliberately structured to mirror
+`test/domains/continuum/runtests.jl`, so any drift between the two
+domains is visible at a glance.
+
+Run with: julia --project=. test/domains/heat/runtests.jl
+"""
+
+using Test
+using JuliaFEM
+using Tensors
+using LinearAlgebra
+
+@testset "Heat Domain Tests" begin
+
+    @testset "Material Trait System" begin
+        @testset "HeatConductivity traits" begin
+            mat = HeatConductivity(k = 50.2)
+            @test material_behavior(mat) isa StatelessConstantTangent
+            @test needs_state(mat) == false
+        end
+    end
+
+    @testset "Kernel through DOF-based assembler" begin
+        # Correctness, KA equivalence, zero-alloc, matrix-free CG, type
+        # stability — single consolidated file so any regression in the
+        # assembler that breaks heat fails on a clearly named test.
+        include("test_heat_kernel.jl")
+    end
+end
+
+println("\n" * "="^70)
+println("HEAT DOMAIN TEST SUMMARY")
+println("="^70)
+println("Test organization:")
+println("  1. Material traits  - Type system verification")
+println("  2. Kernel through DOF-based assembler:")
+println("     - assemble! correctness (symmetry, null space, K vs apply_K!)")
+println("     - KA apply_K! (CPU backend) bit-equivalence")
+println("     - Zero allocation + 0 LLVM gc-alloc sites")
+println("     - Matrix-free CG via LinearOperators (penalty Dirichlet)")
+println("     - Type stability of assemble! + apply_K!")
+println("="^70)