fix: flaky TestSessionBetweenPeers with shuffle enabled (#1022)

* fix: flaky TestSessionBetweenPeers with shuffle enabled

The test was flaky when run with -shuffle=on because of a race condition
in message counting. After fetching the first block (cids[0]), which
triggers a broadcast want-have to all peers and then a CANCEL when
received, the test immediately continued fetching more blocks.

During this time, the session's internal timers (idle tick or periodic
search) could fire and cause a rebroadcast of wants before the test
checked message counts on uninvolved nodes. With test shuffling,
goroutine scheduling changes made this timing issue more likely,
causing uninvolved nodes to sometimes receive 3 messages instead of
the expected 2.

Adding a small delay after the first block fetch ensures the CANCEL
is fully processed and the session stabilizes before continuing,
preventing the race condition.

* Update bitswap/client/bitswap_with_sessions_test.go

---------

Co-authored-by: Andrew Gillis <[email protected]>

Author: lidel

bitswap/client/bitswap_with_sessions_test.go

@@ -203,6 +203,11 @@ func TestSessionBetweenPeers(t *testing.T) {
 	if _, err := ses.GetBlock(ctx, cids[0]); err != nil {
 		t.Fatal(err)
 	}
+
+	// Wait briefly to ensure the CANCEL for cids[0] is fully processed
+	// before continuing with more requests that might trigger rebroadcasts
+	time.Sleep(50 * time.Millisecond)
+
 	blks = blks[1:]
 	cids = cids[1:]