Adding quickcheck for grid graph (Qiskit#1465)

* Adding quickcheck for grid graph

This property test checks structural correctness of grid_graph.

It verifies that the total number of nodes is exactly rows * cols.

It confirms the number of edges matches expectations based on grid dimensions and directionality.
It ensures all edge endpoints refer to valid node indices.

It checks that if the graph is bidirectional, it is weakly connected using BFS traversal.

* Lint issues

Author: Krishn1412

rustworkx-core/tests/quickcheck/grid_graph.rs

@@ -0,0 +1,68 @@
+use petgraph::graph::DiGraph;
+use petgraph::visit::{Bfs, EdgeRef, NodeIndexable};
+use quickcheck::{quickcheck, TestResult};
+use rustworkx_core::generators::grid_graph;
+
+#[test]
+fn prop_grid_graph_validity() {
+    fn prop(rows: usize, cols: usize, bidirectional_flag: bool) -> TestResult {
+        let rows = rows % 32 + 1; // Ensure >= 1
+        let cols = cols % 32 + 1;
+
+        let graph = match grid_graph::<DiGraph<(), ()>, (), _, _, ()>(
+            Some(rows),
+            Some(cols),
+            None,
+            || (),
+            || (),
+            bidirectional_flag,
+        ) {
+            Ok(g) => g,
+            Err(_) => return TestResult::error("Graph generation failed"),
+        };
+
+        let expected_nodes = rows * cols;
+        let base_edges = (rows - 1) * cols + (cols - 1) * rows;
+        let expected_edges = if bidirectional_flag {
+            base_edges * 2
+        } else {
+            base_edges
+        };
+
+        // Property 1: Node count
+        if graph.node_count() != expected_nodes {
+            return TestResult::failed();
+        }
+
+        // Property 2: Edge count
+        if graph.edge_count() != expected_edges {
+            return TestResult::failed();
+        }
+
+        // Property3: All edge indices are in bounds
+        let max_index = graph.node_bound();
+        for edge in graph.edge_references() {
+            let src = edge.source().index();
+            let tgt = edge.target().index();
+            if src >= max_index || tgt >= max_index {
+                return TestResult::failed();
+            }
+        }
+
+        // Property 4: Weak connectivity (if bidirectional, should be connected)
+        if bidirectional_flag {
+            let mut bfs = Bfs::new(&graph, graph.from_index(0));
+            let mut visited = 0;
+            while bfs.next(&graph).is_some() {
+                visited += 1;
+            }
+            if visited != expected_nodes {
+                return TestResult::failed();
+            }
+        }
+
+        TestResult::passed()
+    }
+
+    quickcheck(prop as fn(usize, usize, bool) -> TestResult);
+}

rustworkx-core/tests/quickcheck/special_graph.rs renamed to rustworkx-core/tests/quickcheck/lollipop_graph.rs

@@ -1 +1,2 @@
-mod special_graph;
+mod grid_graph;
+mod lollipop_graph;