Update and adds tests for Graph edge deletion

src/models/graph.rs

@@ -438,6 +438,31 @@ mod tests {
             "unexpected vertex count after delete"
         );
         assert_eq!(graph.edge_count(), 10, "unexpected edge count after delete");
+        let expected_edges = [
+            (vertices[0], vertices[1]),
+            (vertices[1], vertices[3]),
+            (vertices[1], vertices[4]),
+            (vertices[3], vertices[6]),
+            (vertices[4], vertices[7]),
+            (vertices[4], vertices[8]),
+            (vertices[5], vertices[9]),
+            (vertices[6], vertices[9]),
+            (vertices[7], vertices[8]),
+            (vertices[7], vertices[9]),
+        ];
+        for (v, u) in expected_edges {
+            assert!(
+                graph.are_adjacent(v, u),
+                "expected {v:?} and {u:?} to be adjacent after delete"
+            );
+        }
+        for v in [vertices[1], vertices[4], vertices[5], vertices[6]] {
+            assert!(
+                !graph.neighbors(v).any(|u| u == vertices[2]),
+                "unexpected adjacency of {v:?} to deleted vertex {:?}",
+                vertices[2]
+            );
+        }
     }
 
     #[test]
@@ -452,6 +477,20 @@ mod tests {
             "unexpected vertex count before delete"
         );
         assert_eq!(graph.edge_count(), 1, "unexpected edge count before delete");
+        assert!(
+            graph.are_adjacent(v1, v2),
+            "expected vertices to be adjacent before delete"
+        );
+        assert_eq!(
+            graph.degree(v1),
+            1,
+            "unexpected vertex degree before delete"
+        );
+        assert_eq!(
+            graph.degree(v2),
+            1,
+            "unexpected vertex degree before delete"
+        );
         graph.delete_edge(e);
         assert_eq!(
             graph.vertex_count(),
@@ -459,6 +498,98 @@ mod tests {
             "unexpected vertex count after delete"
         );
         assert_eq!(graph.edge_count(), 0, "unexpected edge count after delete");
+        assert!(
+            !graph.are_adjacent(v1, v2),
+            "unexpected adjacency after delete"
+        );
+        assert_eq!(graph.degree(v1), 0, "unexpected vertex degree after delete");
+        assert_eq!(graph.degree(v2), 0, "unexpected vertex degree after delete");
+        assert_ne!(
+            graph.add_edge(v1, v2),
+            e,
+            "unexpected duplicate edge after delete"
+        );
+    }
+
+    #[test]
+    fn delete_edge_loop() {
+        let mut graph = Graph::new();
+        let v = graph.add_vertex();
+        let e = graph.add_edge(v, v);
+        assert_eq!(
+            graph.vertex_count(),
+            1,
+            "unexpected vertex count before delete"
+        );
+        assert_eq!(graph.edge_count(), 1, "unexpected edge count before delete");
+        assert!(
+            graph.are_adjacent(v, v),
+            "expected vertex to be self-adjacent before delete"
+        );
+        assert_eq!(
+            graph.degree(v),
+            2,
+            "unexpected vertex degree before delete"
+        );
+        graph.delete_edge(e);
+        assert_eq!(
+            graph.vertex_count(),
+            1,
+            "unexpected vertex count after delete"
+        );
+        assert_eq!(graph.edge_count(), 0, "unexpected edge count after delete");
+        assert!(
+            !graph.are_adjacent(v, v),
+            "unexpected adjacency after delete"
+        );
+        assert_eq!(graph.degree(v), 0, "unexpected vertex degree after delete");
+        assert_ne!(
+            graph.add_edge(v, v),
+            e,
+            "unexpected duplicate edge after delete"
+        );
+    }
+
+    #[test]
+    fn delete_edge_multiple() {
+        let mut graph = Graph::new();
+        let v1 = graph.add_vertex();
+        let v2 = graph.add_vertex();
+        let e = graph.add_edge(v1, v2);
+        graph.add_edge(v1, v2);
+        assert_eq!(
+            graph.vertex_count(),
+            2,
+            "unexpected vertex count before delete"
+        );
+        assert_eq!(graph.edge_count(), 2, "unexpected edge count before delete");
+        assert!(
+            graph.are_adjacent(v1, v2),
+            "expected vertices to be adjacent before delete"
+        );
+        assert_eq!(
+            graph.degree(v1),
+            2,
+            "unexpected vertex degree before delete"
+        );
+        assert_eq!(
+            graph.degree(v2),
+            2,
+            "unexpected vertex degree before delete"
+        );
+        graph.delete_edge(e);
+        assert_eq!(
+            graph.vertex_count(),
+            2,
+            "unexpected vertex count after delete"
+        );
+        assert_eq!(graph.edge_count(), 1, "unexpected edge count after delete");
+        assert!(
+            graph.are_adjacent(v1, v2),
+            "expected vertices to be adjacent after delete"
+        );
+        assert_eq!(graph.degree(v1), 1, "unexpected vertex degree after delete");
+        assert_eq!(graph.degree(v2), 1, "unexpected vertex degree after delete");
         assert_ne!(
             graph.add_edge(v1, v2),
             e,