Adjust tests to use vitest + jsdom

engine/lib/lerp.test.ts

@@ -0,0 +1,34 @@
+import { expect, test } from "vitest";
+import { lerp, lerpPrecice } from "./lerp.ts";
+
+test("lerp", () => {
+	const a = 0;
+	const b = 0.1;
+
+	expect(lerp(a, b, 0.2)).toBe(0.020000000000000004);
+	expect(lerp(a, b, 0.5)).toBe(0.05);
+});
+
+test("lerpPrecice", () => {
+	const a = 0;
+	const b = 0.1;
+
+	expect(lerpPrecice(a, b, 0.2)).toBe(0.020000000000000004);
+	expect(lerpPrecice(a, b, 0.5)).toBe(0.05);
+});
+
+test("lerp vs lerpPrecice", () => {
+	// a and b with very different magnitudes expose
+	// catastrophic cancellation in lerp's `(b - a)` term
+	const a = 1e16;
+	const b = 1;
+
+	// lerp loses b at t = 1
+	expect(lerp(a, b, 1)).toBe(0);
+
+	// lerpPrecice keeps b at t = 1
+	expect(lerpPrecice(a, b, 1)).toBe(b);
+
+	expect(lerp(a, b, 0)).toBe(a);
+	expect(lerpPrecice(a, b, 0)).toBe(a);
+});