diff --git a/tests/es06_list.rs b/tests/es06_list.rs
index a5b4811..5d8e5fa 100644
--- a/tests/es06_list.rs
+++ b/tests/es06_list.rs
@@ -4,26 +4,33 @@ use esercizi::es06_list::LinkedList;
 fn test_front() {
     let mut list = LinkedList::new();
 
+    assert_eq!(0, list.len());
     assert_eq!(None, list.get_front());
     assert_eq!(None, list.pop_front());
     assert_eq!(None, list.get_front());
+    assert_eq!(0, list.len());
 
     list.push_front(50);
+    assert_eq!(1, list.len());
     assert_eq!(Some(50), list.get_front());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(None, list.get_front());
+    assert_eq!(0, list.len());
 
     list.push_front(50);
     list.push_front(20);
+    assert_eq!(2, list.len());
     assert_eq!(Some(20), list.get_front());
     assert_eq!(Some(20), list.pop_front());
     assert_eq!(Some(50), list.get_front());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(None, list.get_front());
+    assert_eq!(0, list.len());
 
     list.push_front(50);
     list.push_front(20);
     list.push_front(150);
+    assert_eq!(3, list.len());
     assert_eq!(Some(150), list.get_front());
     assert_eq!(Some(150), list.pop_front());
     assert_eq!(Some(20), list.get_front());
@@ -31,32 +38,40 @@ fn test_front() {
     assert_eq!(Some(50), list.get_front());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(None, list.get_front());
+    assert_eq!(0, list.len());
 }
 
 #[test]
 fn test_back() {
     let mut list = LinkedList::new();
 
+    assert_eq!(0, list.len());
     assert_eq!(None, list.get_back());
     assert_eq!(None, list.pop_back());
     assert_eq!(None, list.get_back());
+    assert_eq!(0, list.len());
 
     list.push_back(50);
+    assert_eq!(1, list.len());
     assert_eq!(Some(50), list.get_back());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(None, list.get_back());
+    assert_eq!(0, list.len());
 
     list.push_back(50);
     list.push_back(20);
+    assert_eq!(2, list.len());
     assert_eq!(Some(20), list.get_back());
     assert_eq!(Some(20), list.pop_back());
     assert_eq!(Some(50), list.get_back());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(None, list.get_back());
+    assert_eq!(0, list.len());
 
     list.push_back(50);
     list.push_back(20);
     list.push_back(150);
+    assert_eq!(3, list.len());
     assert_eq!(Some(150), list.get_back());
     assert_eq!(Some(150), list.pop_back());
     assert_eq!(Some(20), list.get_back());
@@ -64,6 +79,7 @@ fn test_back() {
     assert_eq!(Some(50), list.get_back());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(None, list.get_back());
+    assert_eq!(0, list.len());
 }
 
 #[test]
diff --git a/tests/es07_list_generic.rs b/tests/es07_list_generic.rs
index 09be738..a40e1c4 100644
--- a/tests/es07_list_generic.rs
+++ b/tests/es07_list_generic.rs
@@ -15,8 +15,8 @@ fn test_front() {
     assert_eq!(false, list.is_empty());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(true, list.is_empty());
-    assert_eq!(0, list.len());
     assert_eq!(None, list.pop_front());
+    assert_eq!(0, list.len());
 
     list.push_front(50);
     list.push_front(20);
@@ -25,6 +25,7 @@ fn test_front() {
     assert_eq!(Some(20), list.pop_front());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(None, list.pop_front());
+    assert_eq!(0, list.len());
 
     list.push_front(50);
     list.push_front(20);
@@ -35,6 +36,7 @@ fn test_front() {
     assert_eq!(Some(20), list.pop_front());
     assert_eq!(Some(50), list.pop_front());
     assert_eq!(None, list.pop_front());
+    assert_eq!(0, list.len());
 }
 
 #[test]
@@ -52,8 +54,8 @@ fn test_back() {
     assert_eq!(false, list.is_empty());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(true, list.is_empty());
-    assert_eq!(0, list.len());
     assert_eq!(None, list.pop_back());
+    assert_eq!(0, list.len());
 
     list.push_back(50);
     list.push_back(20);
@@ -62,6 +64,7 @@ fn test_back() {
     assert_eq!(Some(20), list.pop_back());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(None, list.pop_back());
+    assert_eq!(0, list.len());
 
     list.push_back(50);
     list.push_back(20);
@@ -72,6 +75,7 @@ fn test_back() {
     assert_eq!(Some(20), list.pop_back());
     assert_eq!(Some(50), list.pop_back());
     assert_eq!(None, list.pop_back());
+    assert_eq!(0, list.len());
 }
 
 #[test]