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

src/testing/fixtures.rs

@@ -58,7 +58,7 @@ impl<G: GraphTopologyAddition> MakeTestGraph for G {
             (vertices[7], vertices[8]),
             (vertices[7], vertices[9]),
         ]
-        .map(|(v1, v2)| (graph.add_edge(v1, v2), v1, v2));
+        .map(|(u, v)| (graph.add_edge(u, v), u, v));
         let i = |vertex, edge| Incidence { vertex, edge };
         let incidences = [
             vec![i(vertices[1], edges[0].0), i(vertices[1], edges[1].0)],
@@ -323,13 +323,13 @@ where
         // Walks the path: tracks current vertex, confirms each edge is incident to it.
         let mut current = source;
         for (i, &e) in path.iter().enumerate() {
-            let (v1, v2) = graph.incident_vertices(e);
-            assert_ne!(v1, v2, "path should not contain loop edge {e:?}");
+            let (u, v) = graph.incident_vertices(e);
+            assert_ne!(u, v, "path should not contain loop edge {e:?}");
             assert!(
-                v1 == current || v2 == current,
-                "path edge {e:?} (index {i}, vertices {v1:?} to {v2:?}) not incident to vertex {current:?}"
+                u == current || v == current,
+                "path edge {e:?} (index {i}, vertices {u:?} to {v:?}) not incident to vertex {current:?}"
             );
-            current = if v1 == current { v2 } else { v1 };
+            current = if u == current { v } else { u };
         }
         assert!(
             targets.contains(&current),