Ok, corrected insert, should have copied directly from my c implementation, all tests good, just need to test insert middle

include/linkedlist.h

@@ -235,37 +235,38 @@ LinkedListErr LinkedList<T>::insert(size_t index, const T& value) {
         return this->append(value);
     }
 
-    if (index >= this->size) {
+    if (index > this->size) {
         return LinkedListErr::LINKEDLIST_OUT_OF_BOUNDS;
     }
 
-    // If index is head
     if (index == 0) {
         return this->prepend(value);
     }
 
-    // If index is tail
-    if (index == this->size - 1) {
+    if (index == this->size) {
         return this->append(value);
     }
 
-    Node<T> *current = this->head;
+    Node<T>* current = this->head;
+
     for (size_t i = 1; i < index; i++) {
         current = current->next;
     }
 
-    Node<T> *new_node = nullptr;
+    Node<T>* new_node = nullptr;
 
     try {
         new_node = new Node<T>;
-    } catch(const std::bad_alloc&) {
+    } catch (const std::bad_alloc&) {
         return LinkedListErr::LINKEDLIST_BAD_ALLOC;
     }
 
     new_node->data = value;
-    new_node->next = current->next->next;
+    new_node->next = current->next;
     current->next = new_node;
 
+    this->size++;
+
     return LinkedListErr::LINKEDLIST_OK;
 }
 

test/test_linkedlist.cpp

@@ -279,3 +279,25 @@ TEST_CASE("Insert at start of list", "[linkedlist]") {
     REQUIRE(list.len() == 4);
     REQUIRE(list.get(0) == 90);
 }
+
+TEST_CASE("Insert at end of list", "[linkedlist]") {
+    LinkedList<int> list = {};
+
+    REQUIRE(list.len() == 0);
+
+    list.append(8);
+    REQUIRE(list.len() == 1);
+    REQUIRE(list.get(0) == 8);
+
+    list.append(9);
+    REQUIRE(list.len() == 2);
+    REQUIRE(list.get(1) == 9);
+
+    list.append(10);
+    REQUIRE(list.len() == 3);
+    REQUIRE(list.get(2) == 10);
+
+    list.insert(2, 90);
+    REQUIRE(list.len() == 4);
+    REQUIRE(list.get(2) == 90);
+}