diff --git a/src/adjacency_list.rs b/src/adjacency_list.rs
index 5c62b19..d2f8b0d 100644
--- a/src/adjacency_list.rs
+++ b/src/adjacency_list.rs
@@ -49,14 +49,16 @@ impl GraphStorage for AdjacencyList {
         }
     }
 
-    fn neighbors(&self, vertex: &Vertex) -> Vec<(Vertex, Edge)> {
+    fn neighbors(&self, vertex: &Vertex) -> Option<Vec<(Vertex, Edge)>> {
         if let Some(neighbors) = self.adj_list.get(vertex) {
-            neighbors
-                .iter()
-                .map(|(v, e)| (v.clone(), e.clone()))
-                .collect()
+            Some(
+                neighbors
+                    .iter()
+                    .map(|(v, e)| (v.clone(), e.clone()))
+                    .collect(),
+            )
         } else {
-            Vec::new()
+            None
         }
     }
 
@@ -68,7 +70,7 @@ impl GraphStorage for AdjacencyList {
         todo!()
     }
 
-    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> bool {
+    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> Option<bool> {
         todo!()
     }
 
@@ -78,7 +80,7 @@ impl GraphStorage for AdjacencyList {
         to: &Vertex,
         old_edge: &crate::storage::Edge,
         new_edge: &crate::storage::Edge,
-    ) -> bool {
+    ) -> Option<bool> {
         todo!()
     }
 }
diff --git a/src/adjacency_matrix.rs b/src/adjacency_matrix.rs
index 46ec06d..e0b9231 100644
--- a/src/adjacency_matrix.rs
+++ b/src/adjacency_matrix.rs
@@ -89,21 +89,27 @@ impl GraphStorage for BinaryAdjMatrix {
         return self.hash.contains_key(from) && self.hash.contains_key(to);
     }
 
-    fn neighbors(&self, vertex: &Vertex) -> Vec<(Vertex, crate::storage::Edge)> {
+    fn neighbors(&self, vertex: &Vertex) -> Option<Vec<(Vertex, Edge)>> {
         todo!()
     }
 
-    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> bool {
-        todo!()
+    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> Option<bool> {
+        let index = self.hash.remove(old_vertex);
+        if index.is_none() {
+            return Some(false);
+        } else {
+            self.hash.insert(new_vertex.clone(), index.unwrap());
+            return Some(true);
+        }
     }
 
     fn set_edge(
         &mut self,
-        from: &Vertex,
-        to: &Vertex,
+        _from: &Vertex,
+        _to: &Vertex,
         _old_edge: &crate::storage::Edge,
         _new_edge: &crate::storage::Edge,
-    ) -> bool {
-        todo!()
+    ) -> Option<bool> {
+        None
     }
 }
diff --git a/src/storage.rs b/src/storage.rs
index 919af4c..3fb54aa 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -52,7 +52,7 @@ pub trait GraphStorage {
     fn edge_size(&self) -> u64;
     fn vertex_size(&self) -> u64;
     fn add_vertex(&mut self, vertex: &Vertex) -> bool;
-    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> bool;
+    fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> Option<bool>;
     fn remove_vertex(&mut self, vertex: &Vertex) -> bool;
     fn add_edge(&mut self, from: &Vertex, to: &Vertex, edge: &Edge) -> bool;
     fn remove_edge(&mut self, from: &Vertex, to: &Vertex, edge: &Edge) -> bool;
@@ -63,7 +63,13 @@ pub trait GraphStorage {
         to: &Vertex,
         old_edge: &crate::storage::Edge,
         new_edge: &crate::storage::Edge,
-    ) -> bool;
+    ) -> Option<bool>;
     fn has_edge(&self, from: &Vertex, to: &Vertex, edge: &Edge) -> bool;
-    fn neighbors(&self, vertex: &Vertex) -> Vec<(Vertex, Edge)>;
+    fn neighbors(&self, vertex: &Vertex) -> Option<Vec<(Vertex, Edge)>>;
 }
+
+#[cfg(test)]
+mod fixed_storage {}
+
+#[cfg(test)]
+mod dynamic_storage {}
diff --git a/src/u_graph.rs b/src/u_graph.rs
index fc23001..f36868d 100644
--- a/src/u_graph.rs
+++ b/src/u_graph.rs
@@ -27,15 +27,15 @@ where
             fn remove_edge(&mut self, from: &Vertex, to: &Vertex, edge: &Edge) -> bool;
             fn has_vertex(&self, vertex: &Vertex) -> bool;
             fn has_edge(&self, from: &Vertex, to: &Vertex, edge: &Edge) -> bool;
-            fn neighbors(&self, vertex: &Vertex) -> Vec<(Vertex, Edge)>;
+            fn neighbors(&self, vertex: &Vertex) -> Option<Vec<(Vertex, Edge)>>;
             fn set_edge(
                 &mut self,
                 from: &Vertex,
                 to: &Vertex,
                 old_edge: &Edge,
                 new_edge: &Edge
-            ) -> bool ;
-            fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> bool;
+            ) -> Option<bool>;
+            fn set_vertex(&mut self, old_vertex: &Vertex, new_vertex: &Vertex) -> Option<bool>;
         }
     }
 }
@@ -59,3 +59,14 @@ where
         UGraph { storage: S::new() }
     }
 }
+#[cfg(test)]
+mod u_graph {
+    use crate::adjacency_matrix::BinaryAdjMatrix;
+
+    use super::*;
+    #[test]
+    fn test() {}
+}
+
+#[test]
+fn a() {}