TEST: add benchmark for extend_from_slice

benches/extend.rs

@@ -40,5 +40,16 @@ fn extend_with_slice(b: &mut Bencher) {
     b.bytes = v.capacity() as u64;
 }
 
-benchmark_group!(benches, extend_with_constant, extend_with_range, extend_with_slice);
+fn extend_with_slice_fn(b: &mut Bencher) {
+    let mut v = ArrayVec::<[u8; 512]>::new();
+    let data = [1; 512];
+    b.iter(|| {
+        v.clear();
+        black_box(v.extend_from_slice(&data));
+        v[0]
+    });
+    b.bytes = v.capacity() as u64;
+}
+
+benchmark_group!(benches, extend_with_constant, extend_with_range, extend_with_slice, extend_with_slice_fn);
 benchmark_main!(benches);