diff --git a/plinth/action_utils.py b/plinth/action_utils.py
index 3e483c14d..d38a393ce 100644
--- a/plinth/action_utils.py
+++ b/plinth/action_utils.py
@@ -356,31 +356,6 @@ def diagnose_url_on_all(url, **kwargs):
     return results
 
 
-def diagnose_netcat(host, port, input='', negate=False):
-    """Run a diagnostic using netcat."""
-    try:
-        process = subprocess.Popen(['nc', host, str(port)],
-                                   stdin=subprocess.PIPE,
-                                   stdout=subprocess.PIPE,
-                                   stderr=subprocess.PIPE)
-        process.communicate(input=input.encode())
-        if process.returncode != 0:
-            result = 'failed'
-        else:
-            result = 'passed'
-
-        if negate:
-            result = 'failed' if result == 'passed' else 'passed'
-    except Exception:
-        result = 'failed'
-
-    test = _('Connect to {host}:{port}')
-    if negate:
-        test = _('Cannot connect to {host}:{port}')
-
-    return [test.format(host=host, port=port), result]
-
-
 def get_addresses():
     """Return a list of IP addresses and hostnames."""
     addresses = get_ip_addresses()
diff --git a/plinth/daemon.py b/plinth/daemon.py
index c867e8171..d48166460 100644
--- a/plinth/daemon.py
+++ b/plinth/daemon.py
@@ -19,6 +19,7 @@ Component for managing a background daemon or any systemd unit.
 """
 
 import socket
+import subprocess
 
 import psutil
 from django.utils.translation import ugettext as _
@@ -158,3 +159,28 @@ def _check_port(port, kind='tcp', listen_address=None):
             return True
 
     return False
+
+
+def diagnose_netcat(host, port, input='', negate=False):
+    """Run a diagnostic using netcat."""
+    try:
+        process = subprocess.Popen(['nc', host, str(port)],
+                                   stdin=subprocess.PIPE,
+                                   stdout=subprocess.PIPE,
+                                   stderr=subprocess.PIPE)
+        process.communicate(input=input.encode())
+        if process.returncode != 0:
+            result = 'failed'
+        else:
+            result = 'passed'
+
+        if negate:
+            result = 'failed' if result == 'passed' else 'passed'
+    except Exception:
+        result = 'failed'
+
+    test = _('Connect to {host}:{port}')
+    if negate:
+        test = _('Cannot connect to {host}:{port}')
+
+    return [test.format(host=host, port=port), result]
diff --git a/plinth/modules/tor/__init__.py b/plinth/modules/tor/__init__.py
index f6ccefb73..bd97e8d2b 100644
--- a/plinth/modules/tor/__init__.py
+++ b/plinth/modules/tor/__init__.py
@@ -25,7 +25,7 @@ from django.utils.translation import ugettext_lazy as _
 from plinth import action_utils, actions
 from plinth import app as app_module
 from plinth import menu
-from plinth.daemon import Daemon, diagnose_port_listening
+from plinth.daemon import Daemon, diagnose_netcat, diagnose_port_listening
 from plinth.modules.firewall.components import Firewall
 from plinth.modules.names.components import DomainType
 from plinth.signals import domain_added, domain_removed
@@ -212,8 +212,8 @@ def _diagnose_control_port():
             negate = False
 
         results.append(
-            action_utils.diagnose_netcat(address['address'], 9051,
-                                         input='QUIT\n', negate=negate))
+            diagnose_netcat(address['address'], 9051, input='QUIT\n',
+                            negate=negate))
 
     return results
 
diff --git a/plinth/tests/test_daemon.py b/plinth/tests/test_daemon.py
index 68c39999b..6a969fa6f 100644
--- a/plinth/tests/test_daemon.py
+++ b/plinth/tests/test_daemon.py
@@ -24,7 +24,8 @@ from unittest.mock import Mock, call, patch
 import pytest
 
 from plinth.app import App, FollowerComponent
-from plinth.daemon import Daemon, app_is_running, diagnose_port_listening
+from plinth.daemon import (Daemon, app_is_running, diagnose_netcat,
+                           diagnose_port_listening)
 
 
 @pytest.fixture(name='daemon')
@@ -210,3 +211,25 @@ def test_diagnose_port_listening(connections):
     assert diagnose_port_listening(3456, 'udp4')[1] == 'passed'
     assert diagnose_port_listening(6789, 'udp4')[1] == 'passed'
     assert diagnose_port_listening(5678, 'udp4')[1] == 'failed'
+
+
+@patch('subprocess.Popen')
+def test_diagnose_netcat(popen):
+    """Test running diagnostic test using netcat."""
+    popen().returncode = 0
+    result = diagnose_netcat('test-host', 3300, input='test-input')
+    assert result == ['Connect to test-host:3300', 'passed']
+    assert popen.mock_calls[1][1] == (['nc', 'test-host', '3300'], )
+    assert popen.mock_calls[2] == call().communicate(input=b'test-input')
+
+    result = diagnose_netcat('test-host', 3300, input='test-input',
+                             negate=True)
+    assert result == ['Cannot connect to test-host:3300', 'failed']
+
+    popen().returncode = 1
+    result = diagnose_netcat('test-host', 3300, input='test-input')
+    assert result == ['Connect to test-host:3300', 'failed']
+
+    result = diagnose_netcat('test-host', 3300, input='test-input',
+                             negate=True)
+    assert result == ['Cannot connect to test-host:3300', 'passed']