protocols/kad/behaviour/test: Fix bootstrap test initialization

When looking for the closest node to a key, Kademlia considers
ALPHA_VALUE nodes to query at initialization. If `num_groups` is larger
than ALPHA_VALUE the remaining locally known nodes will not be
considered. Given that no other node is aware of them other than node 1,
they would be lost entirely. To prevent the above restrict `num_groups`
to be equal or smaller than ALPHA_VALUE.

protocols/kad/src/behaviour/test.rs

@@ -22,7 +22,7 @@
 
 use super::*;
 
-use crate::K_VALUE;
+use crate::{ALPHA_VALUE, K_VALUE};
 use crate::kbucket::Distance;
 use crate::record::store::MemoryStore;
 use futures::{
@@ -136,7 +136,12 @@ fn random_multihash() -> Multihash {
 fn bootstrap() {
     fn run(rng: &mut impl Rng) {
         let num_total = rng.gen_range(2, 20);
-        let num_group = rng.gen_range(1, num_total);
+        // When looking for the closest node to a key, Kademlia considers ALPHA_VALUE nodes to query
+        // at initialization. If `num_groups` is larger than ALPHA_VALUE the remaining locally known
+        // nodes will not be considered. Given that no other node is aware of them, they would be
+        // lost entirely. To prevent the above restrict `num_groups` to be equal or smaller than
+        // ALPHA_VALUE.
+        let num_group = rng.gen_range(1, (num_total % ALPHA_VALUE.get()) + 2);
 
         let mut swarms = build_connected_nodes(num_total, num_group).into_iter()
             .map(|(_a, s)| s)