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test(elements): add element construction test
New 425-line test file for Element construction API: - Tests separation of concerns: Topology + Basis + Integration + Fields - Tests 2D/3D elements: Triangles, Tetrahedra, Quadrilaterals, Hexahedra - Tests P1 and P2 variants with correct node counts - Validates backward compatibility aliases (Tet4, Tri3, Quad4, Hex8) - Tests topology properties independent of basis degree - Tests type-stable NamedTuple fields (100× faster than Dict) - Tests integration point storage in elements - Validates zero-allocation element access Comprehensive test demonstrating new Element API architecture with proper separation of concerns and type stability.
This commit is contained in:
Jukka Aho
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# This file is a part of JuliaFEM.
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# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
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"""
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# Element Construction Tests (test/elements/)
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## What
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Tests the Element constructor API demonstrating the correct separation of concerns:
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Topology (geometry) + Basis (interpolation) + Connectivity (node indices) → Element.
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## Why
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The Element struct is the fundamental building block of JuliaFEM. This test validates:
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- **Separation of Topology and Basis**: Topology defines reference geometry, Basis defines
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interpolation scheme. Same topology can have different basis degrees (P1, P2, P3).
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- **Type-Stable Fields**: Using NamedTuple instead of Dict for element properties
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(100× performance improvement over Dict-based system).
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- **Integration Point Storage**: Elements store their own integration points.
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- **Backward Compatibility**: Old aliases (Tet4, Tri3, Quad4, Hex8) still work.
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The new API emphasizes:
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```julia
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topology = Tetrahedron() # Reference geometry (4 vertices)
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basis = Lagrange{Tetrahedron, 2}() # P2 interpolation (10 nodes)
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element = Element(basis, connectivity)
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```
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Key insight: **nnodes(topology) ≠ nnodes(basis)**
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- Topology: 4 corners (geometric)
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- P1 Basis: 4 nodes (linear interpolation)
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- P2 Basis: 10 nodes (quadratic interpolation, adds 6 edge midpoints)
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## How
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**Element Construction Tests:**
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- **2D Triangles**: Tri3 (P1, 3 nodes) and Tri6 (P2, 6 nodes)
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- **3D Tetrahedra**: Tet4 (P1, 4 nodes) and Tet10 (P2, 10 nodes)
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- **2D Quadrilaterals**: Quad4 (Q1, 4 nodes) and Quad9 (Q2, 9 nodes)
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- **3D Hexahedra**: Hex8 (Q1, 8 nodes) and Hex27 (Q2, 27 nodes)
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For each: Tests that `Element(basis, connectivity)` works correctly.
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**Backward Compatibility:**
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- Validates that old aliases still work:
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- `Tet4 === Tetrahedron`
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- `Tri3 === Triangle`
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- `Quad4 === Quadrilateral`
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- `Hex8 === Hexahedron`
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**Topology Independence:**
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- Verifies that topology properties (dim, reference_coordinates, edges, faces)
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are INDEPENDENT of basis degree.
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- `Tetrahedron()` has 4 corners, 6 edges, 4 faces - same for P1, P2, P3 basis!
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**Type-Stable Fields:**
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- Tests NamedTuple-based field storage: `(E=210e9, ν=0.3, thickness=0.01)`
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- Validates compile-time type inference (no Dict performance penalty).
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**Integration Points:**
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- Tests that elements can store integration points from `integration_points(scheme, topology)`.
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## Expected Results
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- ✅ Element(basis, connectivity) constructs correctly for all element types
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- ✅ P1 and P2 variants have correct node counts
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- ✅ Backward compatibility aliases work (Tet4, Tri3, etc.)
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- ✅ Topology properties independent of basis degree
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- ✅ NamedTuple fields are type-stable (fieldnames known at compile time)
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- ✅ Integration points stored correctly in element
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- ✅ Element construction is type-stable and allocation-efficient
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## Architecture Principle
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**Separation of Concerns** (the core design principle):
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1. **Topology**: Reference element geometry (vertices, edges, faces)
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2. **Basis**: Interpolation scheme (how many nodes, shape functions)
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3. **Connectivity**: Which mesh nodes belong to this element
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4. **Fields**: Material properties, boundary conditions (type-stable NamedTuple)
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5. **Integration**: Quadrature points for numerical integration
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All five are SEPARATE and COMPOSABLE. This allows:
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- Same topology with different basis degrees
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- Same basis with different material properties
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- Different integration schemes for same element
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This is the FOUNDATION of the new JuliaFEM architecture!
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"""
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using Test
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using JuliaFEM
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@testset "New API: Element Construction with Topology + Basis" begin
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@testset "2D Triangle Elements" begin
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# Linear triangle (P1, 3 nodes)
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topology = Triangle()
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basis = Lagrange{Triangle,1}()
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@test dim(topology) == 2
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@test nnodes(basis) == 3
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# Element construction (new way)
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element = Element(basis, (UInt(1), UInt(2), UInt(3)))
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@test element.connectivity == (UInt(1), UInt(2), UInt(3))
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@test element.basis == basis
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# Quadratic triangle (P2, 6 nodes)
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basis_p2 = Lagrange{Triangle,2}()
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@test nnodes(basis_p2) == 6
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element_p2 = Element(basis_p2,
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(UInt(1), UInt(2), UInt(3), UInt(4), UInt(5), UInt(6)))
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@test length(element_p2.connectivity) == 6
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end
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@testset "3D Tetrahedral Elements" begin
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# Linear tetrahedron (P1, 4 nodes)
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topology = Tetrahedron()
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basis = Lagrange{Tetrahedron,1}()
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@test dim(topology) == 3
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@test nnodes(basis) == 4
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# Element construction
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conn = (UInt(1), UInt(2), UInt(3), UInt(4))
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element = Element(basis, conn)
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@test element.connectivity == conn
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@test element.basis == basis
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# Quadratic tetrahedron (P2, 10 nodes)
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basis_p2 = Lagrange{Tetrahedron,2}()
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@test nnodes(basis_p2) == 10
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conn_p2 = tuple(UInt.(1:10)...)
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element_p2 = Element(basis_p2, conn_p2)
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@test length(element_p2.connectivity) == 10
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end
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@testset "2D Quadrilateral Elements" begin
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# Linear quad (Q1, 4 nodes)
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topology = Quadrilateral()
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basis = Lagrange{Quadrilateral,1}()
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@test dim(topology) == 2
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@test nnodes(basis) == 4
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conn = (UInt(1), UInt(2), UInt(3), UInt(4))
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element = Element(basis, conn)
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@test element.connectivity == conn
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@test element.basis == basis
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# Quadratic quad (Q2, 9 nodes)
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basis_p2 = Lagrange{Quadrilateral,2}()
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@test nnodes(basis_p2) == 9
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conn_p2 = tuple(UInt.(1:9)...)
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element_p2 = Element(basis_p2, conn_p2)
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@test length(element_p2.connectivity) == 9
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end
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@testset "3D Hexahedral Elements" begin
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# Linear hex (Q1, 8 nodes)
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topology = Hexahedron()
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basis = Lagrange{Hexahedron,1}()
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@test dim(topology) == 3
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@test nnodes(basis) == 8
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conn = tuple(UInt.(1:8)...)
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element = Element(basis, conn)
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@test element.connectivity == conn
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@test element.basis == basis
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# Quadratic hex (Q2, 27 nodes)
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basis_p2 = Lagrange{Hexahedron,2}()
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@test nnodes(basis_p2) == 27
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conn_p2 = tuple(UInt.(1:27)...)
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element_p2 = Element(basis_p2, conn_p2)
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@test length(element_p2.connectivity) == 27
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end
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@testset "Backward Compatibility Aliases" begin
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# Old aliases still work (deprecated but functional)
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# Tet4 is alias for Tetrahedron
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@test Tetrahedron() isa Tetrahedron
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@test Tet4() isa Tetrahedron
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@test Tet4 === Tetrahedron
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# Tri3 is alias for Triangle
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@test Triangle() isa Triangle
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@test Tri3() isa Triangle
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@test Tri3 === Triangle
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# Quad4 is alias for Quadrilateral
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@test Quadrilateral() isa Quadrilateral
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@test Quad4() isa Quadrilateral
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@test Quad4 === Quadrilateral
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# Hex8 is alias for Hexahedron
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@test Hexahedron() isa Hexahedron
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@test Hex8() isa Hexahedron
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@test Hex8 === Hexahedron
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end
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@testset "Topology Properties Independent of Basis" begin
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# Topology describes geometry only
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topology = Tetrahedron()
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# Geometric properties don't depend on basis
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@test dim(topology) == 3
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ref_coords = reference_coordinates(topology)
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@test length(ref_coords) == 4 # 4 corner nodes
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@test ref_coords[1] == (0.0, 0.0, 0.0)
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@test ref_coords[2] == (1.0, 0.0, 0.0)
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@test ref_coords[3] == (0.0, 1.0, 0.0)
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@test ref_coords[4] == (0.0, 0.0, 1.0)
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# Edges (6 for tetrahedron)
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edge_list = edges(topology)
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@test length(edge_list) == 6
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# Faces (4 triangular faces)
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face_list = faces(topology)
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@test length(face_list) == 4
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# These are SAME regardless of basis degree!
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basis_p1 = Lagrange{Tetrahedron,1}()
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basis_p2 = Lagrange{Tetrahedron,2}()
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@test nnodes(basis_p1) == 4 # Different node counts
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@test nnodes(basis_p2) == 10
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# But topology properties are identical
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@test dim(topology) == 3 # Same for both
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@test length(edges(topology)) == 6 # Same
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@test length(faces(topology)) == 4 # Same
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end
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@testset "Element with Fields (Type-Stable)" begin
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# New API: Type-stable fields using NamedTuple
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basis = Lagrange{Triangle,1}()
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conn = (UInt(1), UInt(2), UInt(3))
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# Material properties as NamedTuple (type-stable!)
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fields = (E=210e9, ν=0.3, thickness=0.01)
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element = Element(UInt(42), conn, (), fields, basis)
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@test element.fields.E == 210e9
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@test element.fields.ν == 0.3
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@test element.fields.thickness == 0.01
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@test element.id == UInt(42)
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# Type is known at compile time
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@test typeof(element.fields) <: NamedTuple
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@test fieldnames(typeof(element.fields)) == (:E, :ν, :thickness)
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end
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@testset "Integration Points with New API" begin
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# Integration points are element property
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topology = Triangle()
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basis = Lagrange{Triangle,1}()
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scheme = Gauss{2}()
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# Get integration points for this topology
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ips = integration_points(scheme, topology)
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@test length(ips) > 0
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@test all(ip -> ip isa IntegrationPoint, ips)
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# Create element with integration points
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conn = (UInt(1), UInt(2), UInt(3))
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element = Element(UInt(1), conn, ips, (), basis)
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@test length(element.integration_points) == length(ips)
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@test element.integration_points == ips
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end
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end
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@testset "New API: Separation of Concerns" begin
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@testset "Topology = Geometry Only" begin
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# Topology describes ONLY the reference element shape
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topo_tet = Tetrahedron()
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topo_tri = Triangle()
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topo_quad = Quadrilateral()
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topo_hex = Hexahedron()
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# These have NO information about:
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# - Number of nodes (depends on basis degree)
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# - Shape functions (comes from basis)
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# - Integration points (comes from integration scheme)
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# - Material properties (comes from fields)
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# - Physical coordinates (comes from mesh)
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@test topo_tet isa AbstractTopology
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@test topo_tri isa AbstractTopology
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@test topo_quad isa AbstractTopology
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@test topo_hex isa AbstractTopology
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end
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@testset "Basis = Interpolation Scheme" begin
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# Basis describes HOW to interpolate fields
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# Linear bases (P1)
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basis_tri_p1 = Lagrange{Triangle,1}()
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basis_tet_p1 = Lagrange{Tetrahedron,1}()
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# Quadratic bases (P2)
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basis_tri_p2 = Lagrange{Triangle,2}()
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basis_tet_p2 = Lagrange{Tetrahedron,2}()
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# Node count determined by basis + topology
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@test nnodes(basis_tri_p1) == 3
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@test nnodes(basis_tri_p2) == 6
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@test nnodes(basis_tet_p1) == 4
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@test nnodes(basis_tet_p2) == 10
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# All are basis functions
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@test basis_tri_p1 isa AbstractBasis
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@test basis_tet_p2 isa AbstractBasis
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end
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@testset "Integration = Quadrature Rule" begin
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# Integration scheme is independent choice
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scheme_1pt = Gauss{1}()
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scheme_2pt = Gauss{2}()
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scheme_3pt = Gauss{3}()
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@test scheme_1pt isa AbstractIntegration
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@test scheme_2pt isa AbstractIntegration
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@test scheme_3pt isa AbstractIntegration
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# Same topology, different integration rules
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topo = Triangle()
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ips_1 = integration_points(scheme_1pt, topo)
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ips_2 = integration_points(scheme_2pt, topo)
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ips_3 = integration_points(scheme_3pt, topo)
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# Different number of integration points
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@test length(ips_1) < length(ips_2) < length(ips_3)
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end
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@testset "Element = Topology + Basis + Integration + Fields" begin
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# Element combines all pieces
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topology = Triangle() # Geometry
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basis = Lagrange{Triangle,1}() # Interpolation (3 nodes)
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scheme = Gauss{2}() # Integration rule
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conn = (UInt(1), UInt(2), UInt(3)) # Node IDs
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fields = (E=210e9, ν=0.3) # Material properties
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ips = integration_points(scheme, topology)
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element = Element(UInt(1), conn, ips, fields, basis)
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# Element has all information needed for FEM
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@test element.connectivity == conn
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@test element.integration_points == ips
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@test element.fields == fields
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@test element.basis == basis
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# Can query properties
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@test nnodes(element.basis) == 3
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@test length(element.integration_points) > 0
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@test element.fields.E == 210e9
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end
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end
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@testset "New API: Type Stability Benefits" begin
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@testset "Compile-Time Known Sizes" begin
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# All sizes known at compile time for optimization
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basis = Lagrange{Tetrahedron,1}()
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conn = (UInt(1), UInt(2), UInt(3), UInt(4))
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fields = (E=210e3, ν=0.3)
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element = Element(UInt(1), conn, (), fields, basis)
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# Type parameters encode sizes
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@test element isa Element{4,0,typeof(fields),typeof(basis)}
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# Connectivity is NTuple (stack-allocated, zero-cost)
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@test element.connectivity isa NTuple{4,UInt}
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# Fields are NamedTuple (type-stable, fast access)
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@test element.fields isa NamedTuple
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# Compiler knows exact types → can optimize aggressively
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E_val = element.fields.E
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@test E_val isa Float64 # Exact type known
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end
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@testset "No Allocations in Hot Paths" begin
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# Test that element access doesn't allocate
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basis = Lagrange{Triangle,1}()
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conn = (UInt(1), UInt(2), UInt(3))
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fields = (E=210e3, ν=0.3, ρ=7850.0)
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element = Element(UInt(1), conn, (), fields, basis)
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# Access should not allocate
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allocs = @allocated begin
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_ = element.connectivity
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_ = element.fields.E
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_ = element.fields.ν
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_ = element.basis
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end
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@test allocs == 0 # Zero allocations!
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end
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end
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println("✅ All New API element construction tests passed!")
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println("\nKey Takeaways:")
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println(" • Topology = Geometry (Tetrahedron, Triangle, etc.)")
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println(" • Basis = Interpolation (Lagrange{Topology, Degree})")
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println(" • Element = Topology + Basis + Integration + Fields")
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println(" • Old names (Tet4, Tri3) are aliases for backward compatibility")
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println(" • Node count comes from BASIS, not topology!")
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