diff --git a/posttroll/backends/zmq/socket.py b/posttroll/backends/zmq/socket.py
index cebfd72..fcc9411 100644
--- a/posttroll/backends/zmq/socket.py
+++ b/posttroll/backends/zmq/socket.py
@@ -1,5 +1,6 @@
 """ZMQ socket handling functions."""
 
+from functools import cache
 from urllib.parse import urlsplit, urlunsplit
 
 import zmq
@@ -101,6 +102,12 @@ def bind(sock, destination, port_interval):
         port_number = port
     return port_number
 
+@cache
+def get_auth_thread(ctx):
+    """Get the authenticator thread for the context."""
+    thr = ThreadAuthenticator(ctx)
+    thr.start()
+    return thr
 
 def create_secure_server_socket(socket_type):
     """Create a secure server socket."""
@@ -109,10 +116,8 @@ def create_secure_server_socket(socket_type):
     authorized_sub_addresses = config.get("authorized_client_addresses", [])
 
     ctx = get_context()
-
     # Start an authenticator for this context.
-    authenticator_thread = ThreadAuthenticator(ctx)
-    authenticator_thread.start()
+    authenticator_thread = get_auth_thread(ctx)
     authenticator_thread.allow(*authorized_sub_addresses)
     # Tell authenticator to use the certificate in a directory
     authenticator_thread.configure_curve(domain="*", location=clients_public_keys_directory)
diff --git a/posttroll/message_broadcaster.py b/posttroll/message_broadcaster.py
index 4990c36..214302b 100644
--- a/posttroll/message_broadcaster.py
+++ b/posttroll/message_broadcaster.py
@@ -43,6 +43,8 @@ def __init__(self, default_port, receivers):
         if backend == "unsecure_zmq":
             from posttroll.backends.zmq.message_broadcaster import ZMQDesignatedReceiversSender
             self._sender = ZMQDesignatedReceiversSender(default_port, receivers)
+        else:
+            raise NotImplementedError()
 
     def __call__(self, data):
         """Send messages from all receivers."""
diff --git a/posttroll/tests/test_nameserver.py b/posttroll/tests/test_nameserver.py
index 88a11ed..bd3f709 100644
--- a/posttroll/tests/test_nameserver.py
+++ b/posttroll/tests/test_nameserver.py
@@ -60,9 +60,6 @@ def create_nameserver_instance(max_age=3, multicast_enabled=True):
         ns.stop()
         thr.join()
 
-def fake_nameserver():
-    config.set(nameserver_port=1111)
-    config.set(address_publish_port())
 
 class TestAddressReceiver(unittest.TestCase):
     """Test the AddressReceiver."""
diff --git a/posttroll/tests/test_secure_zmq_backend.py b/posttroll/tests/test_secure_zmq_backend.py
index f912125..7c4987f 100644
--- a/posttroll/tests/test_secure_zmq_backend.py
+++ b/posttroll/tests/test_secure_zmq_backend.py
@@ -6,8 +6,10 @@
 import time
 from threading import Thread
 
+import pytest
 import zmq.auth
 
+import posttroll.backends.zmq
 from posttroll import config
 from posttroll.backends.zmq import generate_keys
 from posttroll.message import Message
@@ -17,6 +19,15 @@
 from posttroll.tests.test_nameserver import create_nameserver_instance
 
 
+@pytest.fixture(autouse=True)
+def new_context(monkeypatch):
+    """Create a new context for each test."""
+    context = zmq.Context()
+    def get_context():
+        return context
+    monkeypatch.setattr(posttroll.backends.zmq, "get_context", get_context)
+
+
 def create_keys(tmp_path):
     """Create keys."""
     base_dir = tmp_path
@@ -111,8 +122,6 @@ def test_switch_to_secure_zmq_backend(tmp_path):
 
 def test_ipc_pubsub_with_sec_and_factory_sub(tmp_path):
     """Test pub-sub on a secure ipc socket."""
-    # create_keys(tmp_path)
-
     server_public_key_file, server_secret_key_file = zmq.auth.create_certificates(tmp_path, "server")
     client_public_key_file, client_secret_key_file = zmq.auth.create_certificates(tmp_path, "client")