backfill Vec2::rotate tests

crates/cross/src/vec.rs

@@ -144,7 +144,6 @@ impl<R: Real> Vec2<R> {
     //     self.y.to_f64().atan2(self.x.to_f64()).cast()
     // }
 
-    // TODO test
     pub fn rotate(&self, angle: R) -> Self {
         let (sin, cos) = angle.sin_cos();
         let map_1x_0y = Vec2::new(cos, sin);
@@ -492,3 +491,41 @@ impl<R: Real + fmt::Display> fmt::Display for Vec3<R> {
         fmt::Display::fmt(")", f)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use float_eq::assert_float_eq;
+
+    fn assert_vec2(got: Vec2<f32>, want: Vec2<f32>) {
+        assert_float_eq!(got.x(), want.x(), abs <= 1e-6);
+        assert_float_eq!(got.y(), want.y(), abs <= 1e-6);
+    }
+    #[test]
+    fn vec2_rotate_trivial() {
+        // no-op rotate
+        assert_vec2(Vec2::new(1.0, 0.0).rotate(0.0), Vec2::new(1.0, 0.0));
+        assert_vec2(Vec2::new(1.0, 1.0).rotate(f32::two_pi()), Vec2::new(1.0, 1.0));
+        assert_vec2(Vec2::new(-2.0, 3.0).rotate(-f32::two_pi()), Vec2::new(-2.0, 3.0));
+    }
+
+    #[test]
+    fn vec2_rotate_quarter_turns() {
+        assert_vec2(Vec2::new(1.0, 0.0).rotate(f32::pi()), Vec2::new(-1.0, 0.0));
+        assert_vec2(Vec2::new(1.0, -1.0).rotate(f32::pi()), Vec2::new(-1.0, 1.0));
+
+        assert_vec2(Vec2::new(1.0, 0.0).rotate(0.5*f32::pi()), Vec2::new(0.0, 1.0));
+        assert_vec2(Vec2::new(1.0, -1.0).rotate(0.5*f32::pi()), Vec2::new(1.0, 1.0));
+
+        assert_vec2(Vec2::new(-1.0, 0.0).rotate(-0.5*f32::pi()), Vec2::new(0.0, 1.0));
+        assert_vec2(Vec2::new(-1.0, -1.0).rotate(-0.5*f32::pi()), Vec2::new(-1.0, 1.0));
+    }
+
+    #[test]
+    fn vec2_rotate_zero() {
+        assert_vec2(Vec2::new(0.0, 0.0).rotate(1.0), Vec2::new(0.0, 0.0));
+        assert_vec2(Vec2::new(0.0, 0.0).rotate(1e9), Vec2::new(0.0, 0.0));
+    }
+
+    // TODO: lots more Vec, Vec2 tests need backfilling
+}