feat(test): Add unit tests for model instance rendering

tests/unit/model-instance-rendering.test.ts

@@ -0,0 +1,79 @@
+import { BoxGeometry, Mesh, MeshBasicMaterial } from "three";
+import { describe, expect, it } from "vitest";
+
+import {
+  createModelInstanceRenderGroup,
+  disposeModelInstance,
+  syncModelInstanceSelectionShell
+} from "../../src/assets/model-instance-rendering";
+import { createModelInstance } from "../../src/assets/model-instances";
+import type { ModelAssetRecord } from "../../src/assets/project-assets";
+
+const modelAsset: ModelAssetRecord = {
+  id: "asset-model",
+  kind: "model",
+  sourceName: "Model.glb",
+  mimeType: "model/gltf-binary",
+  storageKey: "project-asset:asset-model",
+  byteLength: 1024,
+  metadata: {
+    kind: "model",
+    format: "glb",
+    sceneName: null,
+    nodeCount: 1,
+    meshCount: 1,
+    materialNames: [],
+    textureNames: [],
+    animationNames: [],
+    boundingBox: {
+      min: { x: -1, y: 0, z: -0.5 },
+      max: { x: 1, y: 2, z: 0.5 },
+      size: { x: 2, y: 2, z: 1 }
+    },
+    warnings: []
+  }
+};
+
+function getSelectionShells(group: ReturnType<typeof createModelInstanceRenderGroup>) {
+  return group.children.filter(
+    (child): child is Mesh =>
+      child instanceof Mesh &&
+      child.userData.modelInstanceSelectionShell === true
+  );
+}
+
+describe("model instance rendering", () => {
+  it("toggles one selection shell without replacing unrelated children", () => {
+    const modelInstance = createModelInstance({
+      id: "model-instance",
+      assetId: modelAsset.id
+    });
+    const renderGroup = createModelInstanceRenderGroup(
+      modelInstance,
+      modelAsset,
+      undefined,
+      false
+    );
+    const debugMesh = new Mesh(
+      new BoxGeometry(0.25, 0.25, 0.25),
+      new MeshBasicMaterial()
+    );
+    debugMesh.userData.nonPickable = true;
+    renderGroup.add(debugMesh);
+
+    expect(getSelectionShells(renderGroup)).toHaveLength(0);
+
+    syncModelInstanceSelectionShell(renderGroup, modelAsset, true);
+    syncModelInstanceSelectionShell(renderGroup, modelAsset, true);
+
+    expect(getSelectionShells(renderGroup)).toHaveLength(1);
+    expect(renderGroup.children).toContain(debugMesh);
+
+    syncModelInstanceSelectionShell(renderGroup, modelAsset, false);
+
+    expect(getSelectionShells(renderGroup)).toHaveLength(0);
+    expect(renderGroup.children).toContain(debugMesh);
+
+    disposeModelInstance(renderGroup);
+  });
+});