Fix size bug and add test for it

src/lib.rs

@@ -954,11 +954,10 @@ impl<T> IndexList<T> {
     }
     #[inline]
     fn remove_elem_at_index(&mut self, this: ListIndex) -> Option<T> {
-        this.get()
-            .and_then(|at| {
-                self.size -= 1;
-                self.elems[at].take()
-            })
+        let at = this.get()?;
+        let removed = self.elems[at].take()?;
+        self.size -= 1;
+        Some(removed)
     }
     fn new_node(&mut self, elem: Option<T>) -> ListIndex {
         let reuse = self.free.head;

tests/test.rs

@@ -161,6 +161,16 @@ fn test_single_element() {
     assert_eq!(list.len(), 0);
 }
 #[test]
+fn test_remove_element_twice() {
+    let mut list = IndexList::<u64>::new();
+    let index = list.insert_first(0);
+    let removed1 = list.remove(index);
+    assert_eq!(removed1, Some(0));
+    let removed2 = list.remove(index);
+    assert_eq!(removed2, None);
+    assert_eq!(list.len(), 0);
+}
+#[test]
 fn insert_remove_variants() {
     let count = 256;
     let mut rng = rand::thread_rng();