From d25405b7124393afebda93a54a263ad55aa38aa5 Mon Sep 17 00:00:00 2001
From: Jukka Aho <ahojukka5@gmail.com>
Date: Mon, 11 May 2026 03:02:26 +0300
Subject: [PATCH] test(io): exercise WriteVTK VTU export for structured meshes

Add io tests that load WriteVTK with JuliaFEM and cover stub misuse, Hex8 and
Quad4 VTU output with nodal and cell data, suffix handling, and bad topologies.

- Add test/io/runtests.jl wrapper around the VTK-focused cases
- Implement test_writevtk.jl with structured mesh grids and negative cases
---
 test/io/runtests.jl      |  8 ++++++
 test/io/test_writevtk.jl | 58 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 test/io/runtests.jl
 create mode 100644 test/io/test_writevtk.jl

diff --git a/test/io/runtests.jl b/test/io/runtests.jl
new file mode 100644
index 0000000..86eb75d
--- /dev/null
+++ b/test/io/runtests.jl
@@ -0,0 +1,8 @@
+# SPDX-FileCopyrightText: 2015-2026 Jukka Aho
+# SPDX-License-Identifier: MIT
+
+using Test
+
+@testset "I/O (VTK export)" begin
+    include("test_writevtk.jl")
+end
diff --git a/test/io/test_writevtk.jl b/test/io/test_writevtk.jl
new file mode 100644
index 0000000..89757e4
--- /dev/null
+++ b/test/io/test_writevtk.jl
@@ -0,0 +1,58 @@
+# SPDX-FileCopyrightText: 2015-2026 Jukka Aho
+# SPDX-License-Identifier: MIT
+
+using Test
+using JuliaFEM
+using WriteVTK
+using Tensors: Vec
+
+@testset "write_vtu_mesh stub for non-mesh second argument" begin
+    @test_throws ErrorException write_vtu_mesh("x", 1.0)
+end
+
+@testset "write_vtu_mesh Hex8 + point/cell data" begin
+    mesh = create_structured_box_mesh(Hex8; xmin = 0.0, xmax = 1.0, nx = 2, ymin = 0.0, ymax = 1.0, ny = 1, zmin = 0.0, zmax = 1.0, nz = 1)
+    d = mktempdir()
+    base = joinpath(d, "hex8_out")
+    n = nnodes_total(mesh)
+    ne = nelements(mesh)
+    u = randn(3, n)
+    p = collect(1.0:n)
+    path = write_vtu_mesh(
+        base,
+        mesh;
+        point_data = (; displacement = u, pressure = p),
+        cell_data = (; elem_id = collect(1.0:ne)),
+    )
+    @test endswith(path, ".vtu")
+    @test isfile(path)
+end
+
+@testset "write_vtu_mesh strips .vtu suffix" begin
+    mesh = create_structured_box_mesh(Hex8; xmin = 0.0, xmax = 1.0, nx = 1, ymin = 0.0, ymax = 1.0, ny = 1, zmin = 0.0, zmax = 1.0, nz = 1)
+    d = mktempdir()
+    path = write_vtu_mesh(joinpath(d, "with_suffix.vtu"), mesh)
+    @test isfile(path)
+    @test occursin("with_suffix.vtu", path)
+end
+
+@testset "write_vtu_mesh Quad4" begin
+    mesh = create_structured_box_mesh(Quad4; xmin = 0.0, xmax = 1.0, nx = 2, ymin = 0.0, ymax = 1.0, ny = 2)
+    d = mktempdir()
+    path = write_vtu_mesh(joinpath(d, "quad"), mesh; point_data = (; s = zeros(Float64, nnodes_total(mesh))))
+    @test isfile(path)
+end
+
+@testset "write_vtu_mesh unsupported topology" begin
+    nodes10 = Vec{3,Float64}[
+        Vec(0.0, 0.0, 0.0), Vec(1.0, 0.0, 0.0), Vec(0.0, 1.0, 0.0), Vec(0.0, 0.0, 1.0),
+        Vec(0.5, 0.0, 0.0), Vec(0.5, 0.5, 0.0), Vec(0.0, 0.5, 0.0),
+        Vec(0.0, 0.0, 0.5), Vec(0.5, 0.0, 0.5), Vec(0.0, 0.5, 0.5),
+    ]
+    conn = NTuple{10,UInt32}[
+        ntuple(i -> UInt32(i), 10),
+    ]
+    mesh = Mesh{10,Tet10}(nodes10, conn)
+    d = mktempdir()
+    @test_throws ArgumentError write_vtu_mesh(joinpath(d, "t10"), mesh)
+end