time for a snapshot

workshop/steps/09-slide/slide.test.ts

@@ -0,0 +1,24 @@
+import { expect, test } from "bun:test";
+import { dot, vec } from "./given.ts";
+import { slide } from "./slide.ts";
+
+test("vertical wall kills horizontal motion, keeps vertical", () => {
+	// moving (10,5) into a wall with normal (-1,0)
+	const s = slide(vec(10, 5), vec(-1, 0));
+	expect(s.x).toBeCloseTo(0);
+	expect(s.y).toBeCloseTo(5);
+});
+
+test("horizontal wall kills vertical motion, keeps horizontal", () => {
+	const s = slide(vec(10, 5), vec(0, -1));
+	expect(s.x).toBeCloseTo(10);
+	expect(s.y).toBeCloseTo(0);
+});
+
+test("result always runs along the wall (perpendicular to the normal)", () => {
+	// a diagonal (unit) normal: 0.36 + 0.64 = 1
+	const normal = vec(-0.6, -0.8);
+	const s = slide(vec(10, 0), normal);
+	// the slid velocity has no component into the wall -> dot with normal is 0
+	expect(dot(s, normal)).toBeCloseTo(0);
+});