message: FEAT: Arbitrary StableGraph now can have holes
  Sometimes generate graphs with holes (edges / nodes removed). This helps
  us test things better (and yeah, we found a bug..).
diff: @@ -17,6 +17,7 @@ use graphmap::{
  GraphMap,
  NodeTrait,
  };
  +use visit::NodeIndexable;
  /// `Arbitrary` for `Graph` creates a graph by selecting a node count
  /// and a probability for each possible edge to exist.
  @@ -116,6 +117,16 @@ impl<N, E, Ty, Ix> Arbitrary for StableGraph<N, E, Ty, Ix>
  }
  }
  }
  + if bool::arbitrary(g) {
  + // potentially remove nodes to make holes in nodes & edge sets
  + let n = u8::arbitrary(g) % (gr.node_count() as u8);
  + for _ in 0..n {
  + let ni = node_index(usize::arbitrary(g) % gr.node_bound());
  + if gr.node_weight(ni).is_some() {
  + gr.remove_node(ni);
  + }
  + }
  + }
  gr
  }
  }
  