diff --git a/engine/Scene.ts b/engine/Scene.ts
index 049cb12..58c4d30 100644
--- a/engine/Scene.ts
+++ b/engine/Scene.ts
@@ -1,10 +1,10 @@
-import { box } from "#/engine/Box.ts";
 import {
 	type Process as EntityProcess,
 	entityBlueprintMap,
 	entityProcessMap,
 } from "#/engine/Entity.ts";
 import { type Graph, getNeighbours } from "#/engine/Graph.ts";
+import { box } from "#/engine/lib/box";
 import { type Cache, memoize } from "#/engine/lib/cache.ts";
 import MapArray from "#/engine/lib/MapArray.ts";
 
diff --git a/engine/lib/MapArray.test.ts b/engine/lib/MapArray.test.ts
new file mode 100644
index 0000000..238390a
--- /dev/null
+++ b/engine/lib/MapArray.test.ts
@@ -0,0 +1,27 @@
+import { expect, test } from "vitest";
+import { box } from "./box.ts";
+import MapArray from "./MapArray.ts";
+
+test("MapArray", () => {
+	const mapArray = new MapArray([
+		["a", box(1)],
+		["b", box(2)],
+		["c", box(3)],
+	]);
+	mapArray.set("foo", box(42));
+	mapArray.set("bar", box(0));
+	mapArray.delete("bar");
+
+	expect(mapArray.get("foo")!.value).toBe(42);
+	expect(mapArray.get("bar")).toBe(undefined);
+	expect(mapArray.map.size).toBe(mapArray.array.length);
+	expect(
+		mapArray.entries().reduce(
+			(a, c) => {
+				a[1].value = a[1].value + c[1].value;
+				return a;
+			},
+			["_", box(0)],
+		)[1].value,
+	).toBe(48);
+});
diff --git a/engine/lib/MapArray.ts b/engine/lib/MapArray.ts
index d848e37..633b9a2 100644
--- a/engine/lib/MapArray.ts
+++ b/engine/lib/MapArray.ts
@@ -1,4 +1,4 @@
-import type { Box } from "#/engine/Box.ts";
+import type { Box } from "./box.ts";
 
 export default class MapArray<K, V> {
 	map: Map<K, Box<V>>;
diff --git a/engine/lib/box.test.ts b/engine/lib/box.test.ts
new file mode 100644
index 0000000..9fb4339
--- /dev/null
+++ b/engine/lib/box.test.ts
@@ -0,0 +1,7 @@
+import { expect, test } from "vitest";
+import { type Box, box } from "./box.ts";
+
+test("box", () => {
+	const b: Box<number> = box(42);
+	expect(b).toEqual({ value: 42 });
+});
diff --git a/engine/Box.ts b/engine/lib/box.ts
similarity index 100%
rename from engine/Box.ts
rename to engine/lib/box.ts
diff --git a/engine/system/drawSprites.ts b/engine/system/drawSprites.ts
index c1dba60..f42b353 100644
--- a/engine/system/drawSprites.ts
+++ b/engine/system/drawSprites.ts
@@ -1,4 +1,4 @@
-import type { Box } from "#/engine/Box.ts";
+import type { Box } from "#/engine/lib/box";
 import { sceneChangeSet, sceneComponentsMap } from "#/engine/Scene.ts";
 import { drawSprite, type Sprite, spriteSheetMap } from "#/engine/Sprite.ts";
 import type { Vector } from "#/engine/Vector.ts";