Add tests for Graph::neighbors()

src/models.rs

@@ -214,6 +214,34 @@ mod tests {
         println!("vertices: {:?}", vertices);
     }
 
+    #[test]
+    fn neighbors_empty() {
+        let mut graph = Graph::new();
+        let vertex = graph.add_vertex();
+        assert_eq!(
+            graph.neighbors(vertex).count(),
+            0,
+            "neighbor iterator of vertex with degree 0 should have no elements"
+        );
+    }
+
+    #[test]
+    fn neighbors() {
+        let (graph, vertices) = make_test_graph();
+        // Checks neighbors of vertex 4.
+        assert_eq!(graph.neighbors(vertices[4]).count(), 4, "unexpected vertex count");
+
+        let mut neighbors: Vec<Vertex> = vec![vertices[1], vertices[2], vertices[7], vertices[8]];
+        for v in graph.neighbors(vertices[4]) {
+            if let Some(index) = neighbors.iter().position(|&x| x == v) {
+                neighbors.swap_remove(index);
+            } else {
+                panic!("unexpected vertex of {v:?} from iterator");
+            }
+        }
+        println!("vertices: {:?}", vertices);
+    }
+
     fn make_test_graph() -> (Graph, [Vertex; 10]) {
         let mut graph = Graph::new();
         let vertices: [Vertex; 10] = core::array::from_fn(|_| graph.add_vertex());