Refactor tests: use MakeTestGraph in model-specific tests, deconstruct vertex arrays where useful, adjust local variable names

src/testing/graph_topology_addition_deletion_testing.rs

@@ -50,11 +50,11 @@ pub fn delete_edge_add_edge<G: GraphTopologyDeletion + GraphTopologyAddition>()
 where
     G::Edge: Debug,
 {
-    let (mut graph, vertices, e) = G::single_edge();
+    let (mut graph, [v0, v1], e) = G::single_edge();
     graph.delete_edge(e);
     assert_eq!(graph.edge_count(), 0, "unexpected edge count after delete");
     assert_ne!(
-        graph.add_edge(vertices[0], vertices[1]),
+        graph.add_edge(v0, v1),
         e,
         "unexpected duplicate edge after re-add"
     );