fix test add check for tail value (#148)

Author: DimaYakovenko

2-0-data-structures-and-algorithms/2-2-4-linked-list/src/test/java/com/bobocode/cs/LinkedListTest.java

@@ -407,10 +407,13 @@ void removeLast() {
         int deletedElement = intList.remove(getInternalSize() - 1);
 
         int newLastElement = getInternalElement(getInternalSize() - 1);
+        int tailElement = (int) getNodeValue(TAIL_NODE_FIELD);
+
         int size = getInternalSize();
 
         assertThat(deletedElement).isEqualTo(9);
         assertThat(newLastElement).isEqualTo(8);
+        assertThat(tailElement).isEqualTo(8);
         assertThat(size).isEqualTo(3);
     }
 
@@ -600,4 +603,12 @@ private Field getAccessibleFieldByPredicate(Object object, Predicate<Field> pred
         field.setAccessible(true);
         return field;
     }
+
+    @SneakyThrows
+    private Object getNodeValue(Predicate<Field> predicate) {
+        Object field = getAccessibleFieldByPredicate(intList, predicate).get(intList);
+        final Field value = getAccessibleFieldByPredicate(field, ELEMENT_FIELD);
+        value.setAccessible(true);
+        return value.get(field);
+    }
 }