What about now

lib/xandra/cluster.ex

@@ -334,7 +334,8 @@ defmodule Xandra.Cluster do
     # Internal for testing, not exposed.
     xandra_module: [type: :atom, default: Xandra, doc: false],
     control_connection_module: [type: :atom, default: ControlConnection, doc: false],
-    test_discovered_hosts: [type: :any, default: [], doc: false]
+    test_discovered_hosts: [type: :any, default: [], doc: false],
+    registry_listeners: []
   ]
 
   @start_link_opts_schema_keys Keyword.keys(@start_link_opts_schema)
@@ -633,7 +634,12 @@ defmodule Xandra.Cluster do
     registry_name =
       Module.concat([Xandra.ClusterRegistry, to_string(System.unique_integer([:positive]))])
 
-    {:ok, _} = Registry.start_link(keys: :unique, name: registry_name)
+    {:ok, _} =
+      Registry.start_link(
+        keys: :unique,
+        name: registry_name,
+        listeners: Keyword.fetch!(cluster_opts, :registry_listeners)
+      )
 
     # Start supervisor for the pools.
     {:ok, pool_sup} = Supervisor.start_link([], strategy: :one_for_one)

test/xandra/cluster/ccm_test.exs

@@ -23,9 +23,15 @@ defmodule Xandra.Cluster.CCMTest do
     ccm("start")
     ccm("status")
 
+    Process.register(self(), :this_test_process)
+
     cluster =
       start_supervised!(
-        {Xandra.Cluster, nodes: ["127.0.0.1"], target_pools: 2, sync_connect: 5000}
+        {Xandra.Cluster,
+         nodes: ["127.0.0.1"],
+         target_pools: 2,
+         sync_connect: 5000,
+         registry_listeners: [:this_test_process]}
       )
 
     wait_for_passing(5000, fn ->
@@ -55,13 +61,8 @@ defmodule Xandra.Cluster.CCMTest do
              {{127, 0, 0, 3}, 9042} => %{host: _host3, status: :up}
            } = ctrl_conn_state.peers
 
-    assert [
-             {{{registry_addr1, 9042}, 1}, _pid1, :up},
-             {{{registry_addr2, 9042}, 1}, _pid2, :up}
-           ] =
-             cluster_state.registry
-             |> Registry.select([{{:"$1", :"$2", :"$3"}, [], [{{:"$1", :"$2", :"$3"}}]}])
-             |> Enum.sort()
+    assert_receive {:register, _registry, {{registry_addr1, 9042}, 1}, _pid1, :up}
+    assert_receive {:register, _registry, {{registry_addr2, 9042}, 1}, _pid2, :up}
 
     assert MapSet.subset?(
              MapSet.new([registry_addr1, registry_addr2]),