[VAULT-21282] Expose NetworkLayer on a TestClusterCore via a convenience method for testing purposes (#29659)

Author: kubawi

vault/testing.go

@@ -977,6 +977,14 @@ func (c *TestClusterCore) ClusterListener() *cluster.Listener {
 	return c.getClusterListener()
 }
 
+// NetworkLayer returns the network layer for the cluster core. This can be used
+// in conjunction with the cluster.InmemLayer to disconnect specific nodes from
+// the cluster when we need to simulate abrupt node failure or a network
+// partition in NewTestCluster tests.
+func (c *TestClusterCore) NetworkLayer() cluster.NetworkLayer {
+	return c.Core.clusterNetworkLayer
+}
+
 func (c *TestCluster) Cleanup() {
 	c.Logger.Info("cleaning up vault cluster")
 	if tl, ok := c.Logger.(*corehelpers.TestLogger); ok {