diff --git a/src/models/tiles.test.ts b/src/models/tiles.test.ts
new file mode 100644
index 0000000..091048d
--- /dev/null
+++ b/src/models/tiles.test.ts
@@ -0,0 +1,14 @@
+import { tilesInRange } from "./tiles";
+
+describe("tilesInRange()", () => {
+  /**
+   *     [ ] [X] [X]
+   *   [ ] [X] [.] [X]
+   * [ ] [ ] [X] [X] [ ]
+   *
+   */
+  it("returns tilesID[] in range 1 from origin tile", () => {
+    const got = tilesInRange("1,-2", { range: 1 });
+    expect(got).toEqual(["1,-3", "2,-3", "0,-2", "2,-2", "1,-1", "2,-1"]);
+  });
+});
diff --git a/src/models/tiles.ts b/src/models/tiles.ts
index 42dfdf9..fdca1fb 100644
--- a/src/models/tiles.ts
+++ b/src/models/tiles.ts
@@ -1,3 +1,30 @@
+/**
+ * ```
+ *                      [ ] [ ] [ ] [ ] [ ]
+ *                    [ ] [ ] [ ] [ ] [ ] [ ]
+ *                  [ ] [ ] [ ] [ ] [ ] [ ] [ ]
+ *                [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
+ *                  [ ] [ ] [ ] [ ] [ ] [ ] [ ]
+ *                    [ ] [ ] [ ] [ ] [ ] [ ]
+ *                      [ ] [ ] [ ] [ ] [ ]
+ *
+ *                            =>
+ *
+ *              [-2,-3] [-1,-3] [+0,-3] [1,-3] [2,-3]
+ *
+ *         [-3,-2] [-2,-2] [-1,-2] [+0,-2] [+1,-2] [+2,-2]
+ *
+ *      [-3,-1] [-2,-1] [-1,-1] [+0,-1] [+1,-1] [+2,-1] [+3,-1]
+ *
+ * [-4,+0] [-3,+0] [-2,+0] [-1,+0] [+0,+0] [+1,+0] [+2,+0] [+3,+0]
+ *
+ *      [-3,+1] [-2,+1] [-1,+1] [+0,+1] [+1,+1] [+2,+1] [+3,+1]
+ *
+ *         [-3,+2] [-2,+2] [-1,+2] [+0,+2] [+1,+2] [+2,+2]
+ *
+ *              [-2,+3] [-1,+3] [+0,+3] [1,+3] [2,+3]
+ * ```
+ */
 export const tiles = [
   // 1st row
   "-2,-3",
@@ -75,7 +102,7 @@ export function row(n: -3 | -2 | -1 | 0 | 1 | 2 | 3): TileID[] {
   return tiles.filter((id) => coordinates(id).y === n);
 }
 
-export function tilesInRange(tile: TileID, range = 1): TileID[] {
+export function tilesInRange(tile: TileID, { range } = { range: 1 }): TileID[] {
   const { x, y } = coordinates(tile);
 
   // TODO use range param instead of fixed array?