JuliaFEM.jl/test/test_integration_points_api.jl

# Test: Zero-Allocation Integration Points
# =========================================

using Test
using JuliaFEM
using Tensors
using BenchmarkTools

@testset "Integration Points API" begin
    @testset "Zero Allocation" begin
        # All integration point queries should allocate zero bytes
        @test (@allocated get_gauss_points!(Segment, Gauss{1})) == 0
        @test (@allocated get_gauss_points!(Triangle, Gauss{1})) == 0
        @test (@allocated get_gauss_points!(Tetrahedron, Gauss{1})) == 0
        @test (@allocated get_gauss_points!(Hexahedron, Gauss{2})) == 0
    end

    @testset "Return Type" begin
        # Should return NTuple of (Float64, Vec{D}) pairs
        ips = get_gauss_points!(Triangle, Gauss{1})

        @test isa(ips, Tuple)
        @test length(ips) == 1

        w, ξ = ips[1]
        @test isa(w, Float64)
        @test isa(ξ, Vec{2})
    end

    @testset "Segment" begin
        # 1-point Gauss
        ips = get_gauss_points!(Segment, Gauss{1})
        @test length(ips) == 1
        w, ξ = ips[1]
        @test w ≈ 2.0
        @test ξ[1] ≈ 0.0

        # 2-point Gauss
        ips = get_gauss_points!(Segment, Gauss{2})
        @test length(ips) == 2
        @test sum(ip[1] for ip in ips) ≈ 2.0  # Weights sum to length
    end

    @testset "Triangle" begin
        # 1-point Gauss (centroid)
        ips = get_gauss_points!(Triangle, Gauss{1})
        @test length(ips) == 1
        w, ξ = ips[1]
        @test w ≈ 0.5  # Area of reference triangle
        @test ξ[1] ≈ 1 / 3
        @test ξ[2] ≈ 1 / 3

        # 3-point Gauss
        ips = get_gauss_points!(Triangle, Gauss{2})
        @test length(ips) == 3
        @test sum(ip[1] for ip in ips) ≈ 0.5
    end

    @testset "Tetrahedron" begin
        # 1-point Gauss (centroid)
        ips = get_gauss_points!(Tetrahedron, Gauss{1})
        @test length(ips) == 1
        w, ξ = ips[1]
        @test w ≈ 1 / 6  # Volume of reference tetrahedron
        @test ξ[1] ≈ 0.25
        @test ξ[2] ≈ 0.25
        @test ξ[3] ≈ 0.25

        # 4-point Gauss
        ips = get_gauss_points!(Tetrahedron, Gauss{2})
        @test length(ips) == 4
        @test sum(ip[1] for ip in ips) ≈ 1 / 6
    end

    @testset "Quadrilateral" begin
        # 2×2 Gauss (standard for Q1)
        ips = get_gauss_points!(Quadrilateral, Gauss{2})
        @test length(ips) == 4
        @test sum(ip[1] for ip in ips) ≈ 4.0  # Area of reference quad
    end

    @testset "Hexahedron" begin
        # 2×2×2 Gauss (standard for Hex8)
        ips = get_gauss_points!(Hexahedron, Gauss{2})
        @test length(ips) == 8
        @test sum(ip[1] for ip in ips) ≈ 8.0  # Volume of reference hex
    end
end

@testset "Usage in Assembly Loop" begin
    # Demonstrate zero-allocation assembly pattern
    function assemble_element_stiffness()
        K = 0.0
        for (w, ξ) in get_gauss_points!(Triangle, Gauss{2})
            # Shape functions
            N1 = 1 - ξ[1] - ξ[2]
            N2 = ξ[1]
            N3 = ξ[2]

            # Accumulate (simplified stiffness)
            K += w * (N1^2 + N2^2 + N3^2)
        end
        return K
    end

    # Should allocate zero
    @test (@allocated assemble_element_stiffness()) == 0

    # Verify result is consistent
    K1 = assemble_element_stiffness()
    K2 = assemble_element_stiffness()
    @test K1 ≈ K2
end

@testset "Performance Comparison" begin
    println("\n" * "="^70)
    println("PERFORMANCE: Integration Points vs Old Approach")
    println("="^70)

    # New approach (compile-time, Vec{D})
    new_approach() = begin
        sum_val = 0.0
        for _ in 1:1000
            for (w, ξ) in get_gauss_points!(Triangle, Gauss{2})
                sum_val += w * sum(ξ)
            end
        end
        return sum_val
    end

    println("\nNew approach (compile-time + Vec{D}):")
    display(@benchmark $new_approach())

    println("\n\nExpected: ~1 μs, 0 allocations")
    println("="^70)
end

println("\n✓ All integration point tests passed!")
println("\nUsage Example (NEW API):")
println("```julia")
println("# Zero-allocation loop over integration points:")
println("for (weight, ξ) in get_gauss_points!(Triangle, Gauss{2})")
println("    # NEW API (recommended):")
println("    N = get_basis_functions(Triangle(), Lagrange{1}(), ξ)")
println("    dN = get_basis_derivatives(Triangle(), Lagrange{1}(), ξ)")
println("    # ... compute element matrices")
println("end")
println("```")
println()
println("Note: eval_basis! and eval_dbasis! are DEPRECATED.")
println("Use get_basis_functions and get_basis_derivatives instead.")