Adding Fuzz targets for random graph generator (#1430)

* Adding Fuzz targets for random graph generator

Added a fuzz target for random graph generator with max edges.

* Updates based on comments

Added another test to check determinism (if same graph is returned for the same seed).

* fixing lint issues

* Removing unused imports

---------

Co-authored-by: Ivan Carvalho <[email protected]>

Author: Krishn1412

rustworkx-core/fuzz/Cargo.toml

@@ -34,3 +34,10 @@ path = "fuzz_targets/test_fuzz_bellman_ford.rs"
 test = false
 doc = false
 bench = false
+
+[[bin]]
+name = "test_fuzz_random_graph"
+path = "fuzz_targets/test_fuzz_random_graph.rs"
+test = false
+doc = false
+bench = false

rustworkx-core/fuzz/fuzz_targets/test_fuzz_random_graph.rs

@@ -0,0 +1,71 @@
+#![no_main]
+
+use arbitrary::{Arbitrary, Unstructured};
+use libfuzzer_sys::fuzz_target;
+use rustworkx_core::generators::gnm_random_graph;
+use rustworkx_core::petgraph::graph::DiGraph;
+use rustworkx_core::petgraph::visit::EdgeRef;
+
+#[derive(Debug, Arbitrary)]
+struct GnmInput {
+    n: usize,
+    m: usize,
+    seed: Option<u64>,
+}
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(input) = GnmInput::arbitrary(&mut Unstructured::new(data)) {
+        fuzz_gnm_random_graph(input);
+    }
+});
+
+fn fuzz_gnm_random_graph(input: GnmInput) {
+    if input.n > 512 || input.m > 512 * 512 {
+        return;
+    }
+
+    let max_m = input.n.saturating_mul(input.n.saturating_sub(1));
+    let capped_m = input.m.min(max_m);
+
+    if let Ok(graph1) = gnm_random_graph::<DiGraph<(), ()>, _, _, _, ()>(
+        input.n,
+        capped_m,
+        input.seed,
+        || (),
+        || (),
+    ) {
+        assert_eq!(graph1.node_count(), input.n);
+        assert!(
+            graph1.edge_count() <= max_m,
+            "edge_count {} > max_m {}",
+            graph1.edge_count(),
+            max_m
+        );
+
+        if input.seed.is_some() {
+            if let Ok(graph2) = gnm_random_graph::<DiGraph<(), ()>, _, _, _, ()>(
+                input.n,
+                capped_m,
+                input.seed,
+                || (),
+                || (),
+            ) {
+                assert_eq!(graph1.node_count(), graph2.node_count());
+                assert_eq!(graph1.edge_count(), graph2.edge_count());
+
+                let mut edges1: Vec<_> = graph1
+                    .edge_references()
+                    .map(|e| (e.source().index(), e.target().index()))
+                    .collect();
+                let mut edges2: Vec<_> = graph2
+                    .edge_references()
+                    .map(|e| (e.source().index(), e.target().index()))
+                    .collect();
+
+                edges1.sort_unstable();
+                edges2.sort_unstable();
+                assert_eq!(edges1, edges2, "Graphs differ even with the same seed");
+            }
+        }
+    }
+}