Add unit tests for GraphTopologyDeletion for Graph

src/models/graph.rs

@@ -1,6 +1,6 @@
 use typed_generational_arena::{Arena, Index};
 
-use crate::traits::GraphTopology;
+use crate::traits::{GraphTopology, GraphTopologyDeletion};
 
 type Vertex = Index<VertexIncidenceHeader, usize, usize>;
 
@@ -117,7 +117,16 @@ impl GraphTopology for Graph {
     }
 }
 
-// TODO: impl GraphTopologyDeletion for Graph.
+// TODO: Benchmark delete with storing "previous" in O(1) vs. linear lookup in O(degree).
+impl GraphTopologyDeletion for Graph {
+    fn delete_vertex(&mut self, v: Self::Vertex) {
+        todo!()
+    }
+
+    fn delete_edge(&mut self, e: Self::Edge) {
+        todo!()
+    }
+}
 
 #[cfg(test)]
 mod tests {
@@ -376,6 +385,96 @@ mod tests {
         }
     }
 
+    #[test]
+    fn delete_vertex() {
+        let mut graph = Graph::new();
+        let v = graph.add_vertex();
+        assert_eq!(
+            graph.vertex_count(),
+            1,
+            "unexpected vertex count before delete"
+        );
+        graph.delete_vertex(v);
+        assert_eq!(
+            graph.vertex_count(),
+            0,
+            "unexpected vertex count after delete"
+        );
+        assert_ne!(
+            graph.add_vertex(),
+            v,
+            "unexpected duplicate vertex after delete"
+        );
+    }
+
+    #[test]
+    fn delete_vertex_invalid_index() {
+        let mut graph = Graph::new();
+        let v = graph.add_vertex();
+        graph.delete_vertex(v);
+        let result = std::panic::catch_unwind(move || graph.delete_vertex(v));
+        assert!(result.is_err(), "second deletion should panic");
+    }
+
+    #[test]
+    fn delete_vertex_connected() {
+        let (mut graph, vertices) = make_test_graph();
+        assert_eq!(
+            graph.vertex_count(),
+            10,
+            "unexpected vertex count before delete"
+        );
+        assert_eq!(
+            graph.edge_count(),
+            14,
+            "unexpected edge count before delete"
+        );
+        graph.delete_vertex(vertices[2]);
+        assert_eq!(
+            graph.vertex_count(),
+            9,
+            "unexpected vertex count after delete"
+        );
+        assert_eq!(graph.edge_count(), 10, "unexpected edge count after delete");
+    }
+
+    #[test]
+    fn delete_edge() {
+        let mut graph = Graph::new();
+        let v1 = graph.add_vertex();
+        let v2 = graph.add_vertex();
+        let e = graph.add_edge(v1, v2);
+        assert_eq!(
+            graph.vertex_count(),
+            2,
+            "unexpected vertex count before delete"
+        );
+        assert_eq!(graph.edge_count(), 1, "unexpected edge count before delete");
+        graph.delete_edge(e);
+        assert_eq!(
+            graph.vertex_count(),
+            2,
+            "unexpected vertex count after delete"
+        );
+        assert_eq!(graph.edge_count(), 0, "unexpected edge count after delete");
+        assert_ne!(
+            graph.add_edge(v1, v2),
+            e,
+            "unexpected duplicate edge after delete"
+        );
+    }
+
+    #[test]
+    fn delete_edge_invalid_index() {
+        let mut graph = Graph::new();
+        let v1 = graph.add_vertex();
+        let v2 = graph.add_vertex();
+        let e = graph.add_edge(v1, v2);
+        graph.delete_edge(e);
+        let result = std::panic::catch_unwind(move || graph.delete_edge(e));
+        assert!(result.is_err(), "second deletion should panic");
+    }
+
     fn make_test_graph() -> (Graph, [Vertex; 10]) {
         let mut graph = Graph::new();
         let vertices: [Vertex; 10] = core::array::from_fn(|_| graph.add_vertex());