diff --git a/ros2action/test/test_api.py b/ros2action/test/test_api.py
index 0751d9194..838a5f87d 100644
--- a/ros2action/test/test_api.py
+++ b/ros2action/test/test_api.py
@@ -30,3 +30,78 @@ def test_get_action_clients_and_servers():
 def test_get_action_names():
     with DirectNode(None) as node:
         get_action_names(node=node)
+
+
+def test_action_type_completer():
+    from unittest.mock import Mock, patch
+    from ros2action.api import ActionTypeCompleter
+
+    # Create a mock parsed_args object
+    parsed_args = Mock()
+
+    # Test 1: When action_name_key is None, should return all action types
+    completer = ActionTypeCompleter()
+    with patch('ros2action.api.action_type_completer') as mock_action_type_completer:
+        mock_action_type_completer.return_value = [
+            'example_interfaces/Fibonacci',
+            'action_tutorials_interfaces/Fibonacci'
+        ]
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['example_interfaces/Fibonacci', 'action_tutorials_interfaces/Fibonacci']
+        mock_action_type_completer.assert_called_once()
+
+    # Test 2: When action_name_key is provided and action exists
+    parsed_args.action_name = '/test_action'
+    completer = ActionTypeCompleter(action_name_key='action_name')
+
+    with patch('ros2action.api.NodeStrategy'):
+        with patch('ros2action.api.get_action_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/test_action', ['example_interfaces/Fibonacci']),
+                ('/other_action', ['action_tutorials_interfaces/Fibonacci'])
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['example_interfaces/Fibonacci']
+
+    # Test 3: When action_name_key is provided but action not found
+    parsed_args.action_name = '/nonexistent_action'
+    completer = ActionTypeCompleter(action_name_key='action_name')
+
+    with patch('ros2action.api.NodeStrategy'):
+        with patch('ros2action.api.get_action_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/test_action', ['example_interfaces/Fibonacci']),
+                ('/other_action', ['action_tutorials_interfaces/Fibonacci'])
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == []
+
+
+def test_action_goal_prototype_completer():
+    from unittest.mock import Mock, patch
+    from ros2action.api import ActionGoalPrototypeCompleter
+
+    # Create a mock parsed_args object
+    parsed_args = Mock()
+    parsed_args.action_type = 'example_interfaces/Fibonacci'
+
+    completer = ActionGoalPrototypeCompleter(action_type_key='action_type')
+
+    # Mock the action class and its Goal
+    mock_action_class = Mock()
+    mock_goal_instance = Mock()
+    mock_action_class.Goal.return_value = mock_goal_instance
+
+    with patch('ros2action.api.get_action') as mock_get_action:
+        with patch('ros2action.api.message_to_yaml') as mock_message_to_yaml:
+            mock_get_action.return_value = mock_action_class
+            mock_message_to_yaml.return_value = 'order: 5'
+
+            result = completer(prefix='', parsed_args=parsed_args)
+
+            # Verify get_action was called with the correct action type
+            mock_get_action.assert_called_once_with('example_interfaces/Fibonacci')
+            # Verify message_to_yaml was called with the goal instance
+            mock_message_to_yaml.assert_called_once_with(mock_goal_instance)
+            # Verify the result is a list containing the YAML string
+            assert result == ['order: 5']
diff --git a/ros2component/test/test_api.py b/ros2component/test/test_api.py
index baa14d50f..f2987b9c6 100644
--- a/ros2component/test/test_api.py
+++ b/ros2component/test/test_api.py
@@ -39,3 +39,33 @@ def test_find_container_node_names():
 def test_get_package_component_types():
     """Test get_package_component_types() API function."""
     assert len(get_package_component_types(package_name='ros2component')) == 0
+
+
+def test_component_type_name_completer():
+    from unittest.mock import Mock, patch
+    from ros2component.api import ComponentTypeNameCompleter
+
+    parsed_args = Mock()
+    parsed_args.package_name = 'my_package'
+    completer = ComponentTypeNameCompleter(package_name_key='package_name')
+
+    # Test 1: package has component types
+    with patch('ros2component.api.get_package_component_types') as mock_get_types:
+        mock_get_types.return_value = ['my_package::MyComponent', 'my_package::OtherComponent']
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['my_package::MyComponent', 'my_package::OtherComponent']
+        mock_get_types.assert_called_once_with(package_name='my_package')
+
+    # Test 2: package has no component types
+    with patch('ros2component.api.get_package_component_types') as mock_get_types:
+        mock_get_types.return_value = []
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == []
+
+    # Test 3: different package name
+    parsed_args.package_name = 'other_package'
+    with patch('ros2component.api.get_package_component_types') as mock_get_types:
+        mock_get_types.return_value = ['other_package::Comp']
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['other_package::Comp']
+        mock_get_types.assert_called_once_with(package_name='other_package')
diff --git a/ros2node/test/test_api.py b/ros2node/test/test_api.py
new file mode 100644
index 000000000..7ed60bd9c
--- /dev/null
+++ b/ros2node/test/test_api.py
@@ -0,0 +1,65 @@
+# Copyright 2026 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+def test_node_name_completer():
+    from unittest.mock import Mock, patch
+    from ros2node.api import NodeNameCompleter, NodeName
+
+    parsed_args = Mock()
+
+    # Test 1: no include_hidden_nodes_key, defaults to False
+    completer = NodeNameCompleter()
+    with patch('ros2node.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2node.api.get_node_names') as mock_get_names:
+            mock_get_names.return_value = [
+                NodeName('node1', '/', '/node1'),
+                NodeName('node2', '/ns', '/ns/node2'),
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/node1', '/ns/node2']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_nodes=False)
+
+    # Test 2: include_hidden_nodes_key provided and True
+    parsed_args.include_hidden_nodes = True
+    completer = NodeNameCompleter(include_hidden_nodes_key='include_hidden_nodes')
+    with patch('ros2node.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2node.api.get_node_names') as mock_get_names:
+            mock_get_names.return_value = [
+                NodeName('node1', '/', '/node1'),
+                NodeName('_hidden', '/', '/_hidden'),
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/node1', '/_hidden']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_nodes=True)
+
+    # Test 3: no nodes available
+    parsed_args.include_hidden_nodes = False
+    completer = NodeNameCompleter(include_hidden_nodes_key='include_hidden_nodes')
+    with patch('ros2node.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2node.api.get_node_names') as mock_get_names:
+            mock_get_names.return_value = []
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == []
diff --git a/ros2run/test/test_api.py b/ros2run/test/test_api.py
new file mode 100644
index 000000000..6f71c8327
--- /dev/null
+++ b/ros2run/test/test_api.py
@@ -0,0 +1,45 @@
+# Copyright 2026 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+def test_executable_name_completer():
+    from unittest.mock import Mock, patch
+    from ros2pkg.api import PackageNotFound
+    from ros2run.api import ExecutableNameCompleter
+
+    parsed_args = Mock()
+    parsed_args.package_name = 'my_package'
+    completer = ExecutableNameCompleter(package_name_key='package_name')
+
+    # Test 1: package has executables
+    with patch('ros2run.api.get_executable_paths') as mock_get_paths:
+        mock_get_paths.return_value = [
+            '/opt/ros/humble/lib/my_package/my_exec',
+            '/opt/ros/humble/lib/my_package/other_exec',
+        ]
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['my_exec', 'other_exec']
+        mock_get_paths.assert_called_once_with(package_name='my_package')
+
+    # Test 2: package not found raises PackageNotFound, returns empty list
+    with patch('ros2run.api.get_executable_paths') as mock_get_paths:
+        mock_get_paths.side_effect = PackageNotFound('my_package')
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == []
+
+    # Test 3: package has no executables
+    with patch('ros2run.api.get_executable_paths') as mock_get_paths:
+        mock_get_paths.return_value = []
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == []
diff --git a/ros2service/test/test_api.py b/ros2service/test/test_api.py
new file mode 100644
index 000000000..6207705f1
--- /dev/null
+++ b/ros2service/test/test_api.py
@@ -0,0 +1,128 @@
+# Copyright 2026 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+def test_service_name_completer():
+    from unittest.mock import Mock, patch
+    from ros2service.api import ServiceNameCompleter
+
+    parsed_args = Mock()
+    parsed_args.include_hidden_services = False
+    completer = ServiceNameCompleter(
+        include_hidden_services_key='include_hidden_services')
+
+    # Test 1: returns service names
+    with patch('ros2service.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2service.api.get_service_names') as mock_get_names:
+            mock_get_names.return_value = ['/service1', '/service2']
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/service1', '/service2']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_services=False)
+
+    # Test 2: no services available
+    with patch('ros2service.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2service.api.get_service_names') as mock_get_names:
+            mock_get_names.return_value = []
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == []
+
+    # Test 3: include hidden services
+    parsed_args.include_hidden_services = True
+    with patch('ros2service.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2service.api.get_service_names') as mock_get_names:
+            mock_get_names.return_value = ['/service1', '/_hidden_service']
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/service1', '/_hidden_service']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_services=True)
+
+
+def test_service_type_completer():
+    from unittest.mock import Mock, patch
+    from ros2service.api import ServiceTypeCompleter
+
+    parsed_args = Mock()
+
+    # Test 1: no service_name_key, returns all service types
+    completer = ServiceTypeCompleter()
+    with patch('ros2service.api.service_type_completer') as mock_all_types:
+        mock_all_types.return_value = ['std_srvs/Empty', 'std_srvs/SetBool']
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['std_srvs/Empty', 'std_srvs/SetBool']
+        mock_all_types.assert_called_once()
+
+    # Test 2: service_name_key provided and service found
+    parsed_args.service_name = '/my_service'
+    completer = ServiceTypeCompleter(service_name_key='service_name')
+    with patch('ros2service.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2service.api.get_service_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/my_service', ['std_srvs/Empty']),
+                ('/other_service', ['std_srvs/SetBool']),
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['std_srvs/Empty']
+
+    # Test 3: service_name_key provided but service not found, falls back to all types
+    parsed_args.service_name = '/nonexistent_service'
+    completer = ServiceTypeCompleter(service_name_key='service_name')
+    with patch('ros2service.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2service.api.get_service_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/my_service', ['std_srvs/Empty']),
+            ]
+            with patch('ros2service.api.service_type_completer') as mock_all_types:
+                mock_all_types.return_value = ['std_srvs/Empty', 'std_srvs/SetBool']
+                result = completer(prefix='', parsed_args=parsed_args)
+                assert result == ['std_srvs/Empty', 'std_srvs/SetBool']
+
+
+def test_service_prototype_completer():
+    from unittest.mock import Mock, patch
+    from ros2service.api import ServicePrototypeCompleter
+
+    parsed_args = Mock()
+    parsed_args.service_type = 'std_srvs/SetBool'
+    completer = ServicePrototypeCompleter(service_type_key='service_type')
+
+    mock_service_class = Mock()
+    mock_request_instance = Mock()
+    mock_service_class.Request.return_value = mock_request_instance
+
+    with patch('ros2service.api.get_service') as mock_get_service:
+        with patch('ros2service.api.message_to_yaml') as mock_message_to_yaml:
+            mock_get_service.return_value = mock_service_class
+            mock_message_to_yaml.return_value = 'data: false'
+
+            result = completer(prefix='', parsed_args=parsed_args)
+
+            mock_get_service.assert_called_once_with('std_srvs/SetBool')
+            mock_message_to_yaml.assert_called_once_with(mock_request_instance)
+            assert result == ['data: false']
diff --git a/ros2topic/test/test_api.py b/ros2topic/test/test_api.py
new file mode 100644
index 000000000..94e0a391c
--- /dev/null
+++ b/ros2topic/test/test_api.py
@@ -0,0 +1,127 @@
+# Copyright 2026 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+def test_topic_name_completer():
+    from unittest.mock import Mock, patch
+    from ros2topic.api import TopicNameCompleter
+
+    parsed_args = Mock()
+    parsed_args.include_hidden_topics = False
+    completer = TopicNameCompleter(include_hidden_topics_key='include_hidden_topics')
+
+    # Test 1: returns topic names
+    with patch('ros2topic.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2topic.api.get_topic_names') as mock_get_names:
+            mock_get_names.return_value = ['/topic1', '/topic2']
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/topic1', '/topic2']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_topics=False)
+
+    # Test 2: no topics available
+    with patch('ros2topic.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2topic.api.get_topic_names') as mock_get_names:
+            mock_get_names.return_value = []
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == []
+
+    # Test 3: include hidden topics
+    parsed_args.include_hidden_topics = True
+    with patch('ros2topic.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2topic.api.get_topic_names') as mock_get_names:
+            mock_get_names.return_value = ['/topic1', '/_hidden_topic']
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['/topic1', '/_hidden_topic']
+            mock_get_names.assert_called_once_with(
+                node=mock_node, include_hidden_topics=True)
+
+
+def test_topic_type_completer():
+    from unittest.mock import Mock, patch
+    from ros2topic.api import TopicTypeCompleter
+
+    parsed_args = Mock()
+
+    # Test 1: no topic_name_key, returns all message types
+    completer = TopicTypeCompleter()
+    with patch('ros2topic.api.message_type_completer') as mock_all_types:
+        mock_all_types.return_value = ['std_msgs/String', 'std_msgs/Int32']
+        result = completer(prefix='', parsed_args=parsed_args)
+        assert result == ['std_msgs/String', 'std_msgs/Int32']
+        mock_all_types.assert_called_once()
+
+    # Test 2: topic_name_key provided and topic found
+    parsed_args.topic_name = '/my_topic'
+    completer = TopicTypeCompleter(topic_name_key='topic_name')
+    with patch('ros2topic.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2topic.api.get_topic_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/my_topic', ['std_msgs/String']),
+                ('/other_topic', ['std_msgs/Int32']),
+            ]
+            result = completer(prefix='', parsed_args=parsed_args)
+            assert result == ['std_msgs/String']
+
+    # Test 3: topic_name_key provided but topic not found, falls back to all types
+    parsed_args.topic_name = '/nonexistent_topic'
+    completer = TopicTypeCompleter(topic_name_key='topic_name')
+    with patch('ros2topic.api.NodeStrategy') as mock_node_strategy:
+        mock_node = Mock()
+        mock_node_strategy.return_value.__enter__ = Mock(return_value=mock_node)
+        mock_node_strategy.return_value.__exit__ = Mock(return_value=False)
+        with patch('ros2topic.api.get_topic_names_and_types') as mock_get_names_types:
+            mock_get_names_types.return_value = [
+                ('/my_topic', ['std_msgs/String']),
+            ]
+            with patch('ros2topic.api.message_type_completer') as mock_all_types:
+                mock_all_types.return_value = ['std_msgs/String', 'std_msgs/Int32']
+                result = completer(prefix='', parsed_args=parsed_args)
+                assert result == ['std_msgs/String', 'std_msgs/Int32']
+
+
+def test_topic_message_prototype_completer():
+    from unittest.mock import Mock, patch
+    from ros2topic.api import TopicMessagePrototypeCompleter
+
+    parsed_args = Mock()
+    parsed_args.message_type = 'std_msgs/String'
+    completer = TopicMessagePrototypeCompleter(topic_type_key='message_type')
+
+    mock_message_class = Mock()
+    mock_message_instance = Mock()
+    mock_message_class.return_value = mock_message_instance
+
+    with patch('ros2topic.api.get_message') as mock_get_message:
+        with patch('ros2topic.api.message_to_yaml') as mock_message_to_yaml:
+            mock_get_message.return_value = mock_message_class
+            mock_message_to_yaml.return_value = 'data: ""'
+
+            result = completer(prefix='', parsed_args=parsed_args)
+
+            mock_get_message.assert_called_once_with('std_msgs/String')
+            mock_message_to_yaml.assert_called_once_with(mock_message_instance)
+            assert result == ["'data: \"\"'"]