rasata
diff --git a/‎graphs/graph_adjacency_list.py‎
Lines changed: 9 additions & 0 deletions b/‎graphs/graph_adjacency_list.py‎
Lines changed: 9 additions & 0 deletions
@@ -61,6 +61,15 @@ def add_vertex(self, vertex: T) -> None:
         """
         Adds a vertex to the graph. If the given vertex already exists,
         a ValueError will be thrown.
+
+        >>> g = GraphAdjacencyList(vertices=[], edges=[], directed=False)
+        >>> g.add_vertex("A")
+        >>> g.adj_list
+        {'A': []}
+        >>> g.add_vertex("A")
+        Traceback (most recent call last):
+        ...
+        ValueError: Incorrect input: A is already in the graph.
         """
         if self.contains_vertex(vertex):
             msg = f"Incorrect input: {vertex} is already in the graph."