test: add coverage for clampHorizontalSpeed and projectDirectionOnPlane

src/movement/__tests__/MovementMath.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import { Vector3 } from 'three';
-import { accelerate, applyFriction, clipVelocity } from '../MovementMath';
+import { accelerate, applyFriction, clipVelocity, clampHorizontalSpeed, projectDirectionOnPlane } from '../MovementMath';
 
 describe('MovementMath', () => {
   it('accelerate increases speed toward wishdir up to addSpeed', () => {
@@ -24,3 +24,63 @@ describe('MovementMath', () => {
     expect(clipped.y).toBeGreaterThanOrEqual(-1e-5);
   });
 });
+
+describe('clampHorizontalSpeed', () => {
+  it('does not modify velocity already under the limit', () => {
+    const vel = new Vector3(3, 5, 0); // horizontal speed = 3, under limit of 10
+    const result = clampHorizontalSpeed(vel, 10);
+    expect(result.x).toBeCloseTo(3);
+    expect(result.z).toBeCloseTo(0);
+    expect(result.y).toBeCloseTo(5); // vertical unchanged
+  });
+
+  it('clamps horizontal speed to the limit when over', () => {
+    const vel = new Vector3(6, 0, 8); // horizontal speed = 10, limit = 5
+    const result = clampHorizontalSpeed(vel, 5);
+    expect(Math.hypot(result.x, result.z)).toBeCloseTo(5);
+    expect(result.y).toBeCloseTo(0); // vertical unchanged
+  });
+
+  it('preserves direction when clamping', () => {
+    const vel = new Vector3(6, 2, 8); // horizontal speed = 10
+    const result = clampHorizontalSpeed(vel, 5);
+    // Direction ratio x/z should be preserved
+    expect(result.x / result.z).toBeCloseTo(vel.x / vel.z);
+  });
+
+  it('handles zero vector without division by zero', () => {
+    const vel = new Vector3(0, 0, 0);
+    const result = clampHorizontalSpeed(vel, 10);
+    expect(result.x).toBeCloseTo(0);
+    expect(result.z).toBeCloseTo(0);
+  });
+});
+
+describe('projectDirectionOnPlane', () => {
+  it('returns a normalized vector perpendicular to the normal', () => {
+    const dir = new Vector3(1, 1, 0).normalize();
+    const normal = new Vector3(0, 1, 0);
+    const result = projectDirectionOnPlane(dir, normal);
+    // Result should be unit length
+    expect(result.length()).toBeCloseTo(1);
+    // Result should be perpendicular to the normal (dot product ≈ 0)
+    expect(result.dot(normal)).toBeCloseTo(0);
+  });
+
+  it('returns zero vector when direction is parallel to normal', () => {
+    const dir = new Vector3(0, 1, 0); // same direction as normal
+    const normal = new Vector3(0, 1, 0);
+    const result = projectDirectionOnPlane(dir, normal);
+    expect(result.length()).toBeCloseTo(0);
+  });
+
+  it('does not mutate input vectors', () => {
+    const dir = new Vector3(1, 1, 0).normalize();
+    const normal = new Vector3(0, 1, 0);
+    const dirBefore = dir.clone();
+    const normalBefore = normal.clone();
+    projectDirectionOnPlane(dir, normal);
+    expect(dir.equals(dirBefore)).toBe(true);
+    expect(normal.equals(normalBefore)).toBe(true);
+  });
+});