Adding quickcheck for petersen graph (#1485)

Testing the following to ensure structural property are met:
1) nodes are 2n
2) edges are 3n
3) no self loop
4) nodes are within bounds

Author: Krishn1412

rustworkx-core/tests/quickcheck/main.rs

@@ -11,3 +11,4 @@ mod hexagonal_lattice_graph;
 mod karate_club;
 mod lollipop_graph;
 mod path_graph;
+mod petersen_graph;

rustworkx-core/tests/quickcheck/petersen_graph.rs

@@ -0,0 +1,53 @@
+#[cfg(test)]
+mod tests {
+    use petgraph::graph::UnGraph;
+    use petgraph::visit::EdgeRef;
+    use quickcheck::{quickcheck, TestResult};
+
+    use rustworkx_core::generators::petersen_graph;
+
+    #[test]
+    fn prop_petersen_graph_structure() {
+        fn prop(n_in: u8, k_in: u8) -> TestResult {
+            let n = (n_in as usize % 97).max(3); // n >= 3
+            let k = ((k_in as usize) % n).max(1); // k >= 1
+
+            // Discard invalid input: k must be < n/2
+            if k >= n / 2 {
+                return TestResult::discard();
+            }
+
+            let g: UnGraph<(), ()> = match petersen_graph(n, k, || (), || ()) {
+                Ok(graph) => graph,
+                Err(_) => return TestResult::failed(),
+            };
+
+            // node_count should be exactly 2n
+            if g.node_count() != 2 * n {
+                return TestResult::failed();
+            }
+
+            // edge_count should be exactly 3n
+            if g.edge_count() != 3 * n {
+                return TestResult::failed();
+            }
+
+            // No self-loops
+            if g.edge_references().any(|e| e.source() == e.target()) {
+                return TestResult::failed();
+            }
+
+            // All node indices must be within bounds
+            let max_node = g.node_count();
+            for edge in g.edge_references() {
+                if edge.source().index() >= max_node || edge.target().index() >= max_node {
+                    return TestResult::failed();
+                }
+            }
+
+            TestResult::passed()
+        }
+
+        quickcheck(prop as fn(u8, u8) -> TestResult);
+    }
+}