diff --git a/packages/timestep/test/index.ts b/packages/timestep/test/index.ts
index 7d2d189391..ea69f19c2b 100644
--- a/packages/timestep/test/index.ts
+++ b/packages/timestep/test/index.ts
@@ -1,7 +1,39 @@
 import { group } from "@thi.ng/testament";
-// import * as assert from "assert";
-// import { } from "../src/index.js";
+import { eqDelta } from "@thi.ng/math";
+import * as assert from "assert";
+import {
+	defNumeric,
+	defTimeStep,
+	defVector2,
+	defVector3,
+	defVector4,
+} from "../src/index.js";
+import { eqDelta2, maddN2, maddN3, maddN4 } from "@thi.ng/vectors";
 
 group("timestep", {
+	numeric: () => {
+		const sim = defTimeStep({ maxFrameTime: 10 });
+		const states = [
+			defNumeric(100, (x, dt) => x - 0.1 * dt),
+			defNumeric(0, (x, dt) => (100 - x) * 0.1 * dt),
+		];
+		sim.update(61 * (1000 / 60), states);
+		assert.ok(eqDelta(states[0].deref(), 99.9, 0.001));
+		assert.ok(eqDelta(states[1].deref(), 0.166, 0.001));
+	},
 
+	vector: () => {
+		const sim = defTimeStep({ maxFrameTime: 10 });
+		const states = [
+			defVector2([0, 0], (v, dt) => maddN2(v, [-10, 20], dt, v)),
+			defVector3([0, 0, 0], (v, dt) => maddN3(v, [-10, 20, -30], dt, v)),
+			defVector4([0, 0, 0, 0], (v, dt) =>
+				maddN4(v, [-10, 20, -30, 40], dt, v)
+			),
+		];
+		sim.update(61 * (1000 / 60), states);
+		assert.ok(eqDelta2(states[0].deref(), [-10, 20], 0.001));
+		assert.ok(eqDelta2(states[1].deref(), [-10, 20, -30], 0.001));
+		assert.ok(eqDelta2(states[2].deref(), [-10, 20, -30, 40], 0.001));
+	},
 });