Add more tests.

lib/point.test.tsx

@@ -0,0 +1,21 @@
+import { normalizePoint } from "./point";
+
+describe("normalizePoint()", () => {
+  it("Does nothing to points w/ length 1", () => {
+    expect(normalizePoint({ x: 1, y: 0 })).toEqual({ x: 1, y: 0 });
+    expect(normalizePoint({ x: 0, y: 1 })).toEqual({ x: 0, y: 1 });
+  });
+
+  it("Raises an exception on points w/ length 0", () => {
+    expect(() => normalizePoint({ x: 0, y: 0 })).toThrow(
+      "Unable to normalize point with length 0"
+    );
+  });
+
+  it("Normalizes points", () => {
+    expect(normalizePoint({ x: 1, y: 1 })).toEqual({
+      x: 1 / Math.sqrt(2),
+      y: 1 / Math.sqrt(2),
+    });
+  });
+});

lib/point.ts

@@ -9,6 +9,9 @@ export function subtractPoints(p1: Point, p2: Point): Point {
 
 export function normalizePoint(p: Point): Point {
   const len = Math.sqrt(Math.pow(p.x, 2) + Math.pow(p.y, 2));
+  if (len === 0) {
+    throw new Error(`Unable to normalize point with length 0`);
+  }
   return {
     x: p.x / len,
     y: p.y / len,