diff --git a/tests/domain/custom-material.command.test.ts b/tests/domain/custom-material.command.test.ts
new file mode 100644
index 00000000..6d8c5508
--- /dev/null
+++ b/tests/domain/custom-material.command.test.ts
@@ -0,0 +1,234 @@
+import { describe, expect, it } from "vitest";
+
+import { createEditorStore } from "../../src/app/editor-store";
+import { createCreateBoxBrushCommand } from "../../src/commands/create-box-brush-command";
+import { createCreateCustomMaterialCommand } from "../../src/commands/create-custom-material-command";
+import { createSetCustomMaterialTextureCommand } from "../../src/commands/set-custom-material-texture-command";
+import { createUpdateCustomMaterialCommand } from "../../src/commands/update-custom-material-command";
+import {
+  createProjectAssetStorageKey,
+  type ImageAssetRecord
+} from "../../src/assets/project-assets";
+import {
+  BOX_FACE_IDS,
+  type WhiteboxFaceId
+} from "../../src/document/brushes";
+import { createCustomMaterialDef } from "../../src/materials/starter-material-library";
+
+function createImageAsset(id: string): ImageAssetRecord {
+  return {
+    id,
+    kind: "image",
+    sourceName: `${id}.png`,
+    mimeType: "image/png",
+    storageKey: createProjectAssetStorageKey(id),
+    byteLength: 128,
+    metadata: {
+      kind: "image",
+      width: 4,
+      height: 4,
+      hasAlpha: false,
+      warnings: []
+    }
+  };
+}
+
+describe("custom material commands", () => {
+  it("creates a custom material and applies it to the selected face with undo/redo", () => {
+    const store = createEditorStore();
+    const material = createCustomMaterialDef({
+      id: "material-custom-face",
+      name: "Blue Test",
+      albedoColorHex: "#3366ff"
+    });
+
+    store.executeCommand(createCreateBoxBrushCommand());
+
+    const brush = Object.values(store.getState().document.brushes)[0];
+
+    store.executeCommand(
+      createCreateCustomMaterialCommand({
+        material,
+        applyTo: {
+          kind: "face",
+          brushId: brush.id,
+          faceId: "posZ"
+        }
+      })
+    );
+
+    expect(store.getState().document.materials[material.id]).toMatchObject({
+      kind: "custom",
+      name: "Blue Test",
+      albedoColorHex: "#3366ff"
+    });
+    expect(
+      store.getState().document.brushes[brush.id].faces.posZ.materialId
+    ).toBe(material.id);
+    expect(store.getState().selection).toEqual({
+      kind: "brushFace",
+      brushId: brush.id,
+      faceId: "posZ"
+    });
+
+    expect(store.undo()).toBe(true);
+    expect(store.getState().document.materials[material.id]).toBeUndefined();
+    expect(
+      store.getState().document.brushes[brush.id].faces.posZ.materialId
+    ).toBeNull();
+
+    expect(store.redo()).toBe(true);
+    expect(store.getState().document.materials[material.id]).toBeDefined();
+    expect(
+      store.getState().document.brushes[brush.id].faces.posZ.materialId
+    ).toBe(material.id);
+  });
+
+  it("creates a custom material and applies it to all selected solid faces", () => {
+    const store = createEditorStore();
+    const material = createCustomMaterialDef({
+      id: "material-custom-solid",
+      name: "Solid Test"
+    });
+
+    store.executeCommand(createCreateBoxBrushCommand());
+
+    const brush = Object.values(store.getState().document.brushes)[0];
+
+    store.executeCommand(
+      createCreateCustomMaterialCommand({
+        material,
+        applyTo: {
+          kind: "brush",
+          brushId: brush.id
+        }
+      })
+    );
+
+    for (const faceId of BOX_FACE_IDS) {
+      expect(
+        store.getState().document.brushes[brush.id].faces[
+          faceId as WhiteboxFaceId
+        ].materialId
+      ).toBe(material.id);
+    }
+
+    expect(store.undo()).toBe(true);
+
+    for (const faceId of BOX_FACE_IDS) {
+      expect(
+        store.getState().document.brushes[brush.id].faces[
+          faceId as WhiteboxFaceId
+        ].materialId
+      ).toBeNull();
+    }
+  });
+
+  it("updates custom material scalar settings and restores them on undo", () => {
+    const store = createEditorStore();
+    const material = createCustomMaterialDef({
+      id: "material-custom-update",
+      roughness: 0.8,
+      metallic: 0
+    });
+
+    store.executeCommand(
+      createCreateCustomMaterialCommand({
+        material
+      })
+    );
+    store.executeCommand(
+      createUpdateCustomMaterialCommand({
+        materialId: material.id,
+        update: {
+          opacity: 0.45,
+          roughness: 0.2,
+          metallic: 0.9,
+          normalStrength: 0.35
+        }
+      })
+    );
+
+    expect(store.getState().document.materials[material.id]).toMatchObject({
+      opacity: 0.45,
+      roughness: 0.2,
+      metallic: 0.9,
+      normalStrength: 0.35
+    });
+
+    expect(store.undo()).toBe(true);
+    expect(store.getState().document.materials[material.id]).toMatchObject({
+      opacity: 1,
+      roughness: 0.8,
+      metallic: 0,
+      normalStrength: 1
+    });
+  });
+
+  it("imports and assigns image texture assets to custom material slots", () => {
+    const store = createEditorStore();
+    const material = createCustomMaterialDef({
+      id: "material-custom-texture"
+    });
+    const imageAsset = createImageAsset("asset-material-albedo");
+
+    store.executeCommand(
+      createCreateCustomMaterialCommand({
+        material
+      })
+    );
+    store.executeCommand(
+      createSetCustomMaterialTextureCommand({
+        materialId: material.id,
+        slot: "albedo",
+        assetId: imageAsset.id,
+        asset: imageAsset
+      })
+    );
+
+    const assignedMaterial = store.getState().document.materials[material.id];
+
+    expect(store.getState().document.assets[imageAsset.id]).toEqual(imageAsset);
+    expect(assignedMaterial).toMatchObject({
+      kind: "custom",
+      textures: {
+        albedo: {
+          assetId: imageAsset.id
+        }
+      }
+    });
+
+    expect(store.undo()).toBe(true);
+    expect(store.getState().document.assets[imageAsset.id]).toBeUndefined();
+    expect(store.getState().document.materials[material.id]).toMatchObject({
+      textures: {
+        albedo: null
+      }
+    });
+
+    expect(store.redo()).toBe(true);
+    expect(store.getState().document.assets[imageAsset.id]).toEqual(imageAsset);
+    expect(store.getState().document.materials[material.id]).toMatchObject({
+      textures: {
+        albedo: {
+          assetId: imageAsset.id
+        }
+      }
+    });
+  });
+
+  it("keeps starter materials read-only", () => {
+    const store = createEditorStore();
+
+    expect(() =>
+      store.executeCommand(
+        createUpdateCustomMaterialCommand({
+          materialId: "starter-amber-grid",
+          update: {
+            roughness: 0.4
+          }
+        })
+      )
+    ).toThrow("Starter materials are read-only.");
+  });
+});