diff --git a/README.md b/README.md
index ffc6a8d8..19418186 100644
--- a/README.md
+++ b/README.md
@@ -154,7 +154,7 @@ Then you can run pytest.
 Notes:
 
 - Make sure to use the python3 instance of pytest from inside the environment.
-- The tests include an nvidia test which assumes you're using a machine with an nvidia gpu.
+- The tests include an nvidia test which assumes you're using a machine with an nvidia gpu. To skip them use `-m "not nvidia"`
 
 
 # Example usage
diff --git a/src/rocker/rmw_extension.py b/src/rocker/rmw_extension.py
index 93d440c9..5cef594f 100644
--- a/src/rocker/rmw_extension.py
+++ b/src/rocker/rmw_extension.py
@@ -42,7 +42,10 @@ def __init__(self):
         self.name = RMW.get_name()
 
     def get_docker_args(self, cli_args):
-        implementation = cli_args.get('rmw')[0]
+        rmw_config = cli_args.get('rmw')
+        if not rmw_config:
+            return '' # not active
+        implementation = rmw_config[0]
         args = f' -e RMW_IMPLEMENTATION=rmw_{implementation}_cpp'
         return args #% self.get_environment_subs()
 
@@ -61,6 +64,8 @@ def get_snippet(self, cliargs):
         rmw = cliargs.get('rmw', None)
         if rmw:
             rmw = rmw[0]
+        else:
+            return '' # rmw not active
         data['rmw'] = rmw
         data['packages'] = RMW.get_package_names(rmw)
         # data['rosdistro'] = 'rolling'
diff --git a/src/rocker/templates/rmw_snippet.Dockerfile.em b/src/rocker/templates/rmw_snippet.Dockerfile.em
index f5bb97c0..87f50275 100644
--- a/src/rocker/templates/rmw_snippet.Dockerfile.em
+++ b/src/rocker/templates/rmw_snippet.Dockerfile.em
@@ -10,7 +10,7 @@ RUN \
      @(' '.join(packages)) \
    && apt-get clean ;\
   else \
-   echo "Found rmw implementation no need to install" ; \
+   echo "Found rmw packages @(' '.join(packages)) no need to install" ; \
   fi
 @[ end if ]@
 
diff --git a/test/test_rmw_extension.py b/test/test_rmw_extension.py
new file mode 100644
index 00000000..faebe6a1
--- /dev/null
+++ b/test/test_rmw_extension.py
@@ -0,0 +1,95 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+import em
+import os
+import unittest
+import pytest
+
+
+from rocker.core import DockerImageGenerator
+from rocker.core import list_plugins
+
+from test_extension import plugin_load_parser_correctly
+
+
+
+class rmwExtensionTest(unittest.TestCase):
+
+    def setUp(self):
+        # Work around interference between empy Interpreter
+        # stdout proxy and test runner. empy installs a proxy on stdout
+        # to be able to capture the information.
+        # And the test runner creates a new stdout object for each test.
+        # This breaks empy as it assumes that the proxy has persistent
+        # between instances of the Interpreter class
+        # empy will error with the exception
+        # "em.Error: interpreter stdout proxy lost"
+        em.Interpreter._wasProxyInstalled = False
+
+    def test_rmw_extension(self):
+        plugins = list_plugins()
+        rmw_plugin = plugins['rmw']
+        self.assertEqual(rmw_plugin.get_name(), 'rmw')
+
+        p = rmw_plugin()
+        self.assertTrue(plugin_load_parser_correctly(rmw_plugin))
+        
+
+        mock_cliargs = {'rmw': ['cyclonedds']}
+        # TODO self.assertEqual(p.get_snippet(mock_cliargs), '')
+        self.assertEqual(p.get_preamble(mock_cliargs), '')
+        args = p.get_docker_args(mock_cliargs)
+        self.assertIn('-e RMW_IMPLEMENTATION=rmw_cyclonedds_cpp', args)
+        snippet = p.get_snippet(mock_cliargs)
+        self.assertIn('rmw-cyclonedds-cpp', snippet)
+
+
+        #without it set
+        mock_cliargs = {'rmw': None}
+        args = p.get_docker_args(mock_cliargs)
+        snippet = p.get_snippet(mock_cliargs)
+        self.assertNotIn('RMW_IMPLEMENTATION', args)
+        self.assertNotIn('rmw-cyclonedds-cpp', snippet)
+
+
+@pytest.mark.docker
+class rmwRuntimeExtensionTest(unittest.TestCase):
+
+    def setUp(self):
+        # Work around interference between empy Interpreter
+        # stdout proxy and test runner. empy installs a proxy on stdout
+        # to be able to capture the information.
+        # And the test runner creates a new stdout object for each test.
+        # This breaks empy as it assumes that the proxy has persistent
+        # between instances of the Interpreter class
+        # empy will error with the exception
+        # "em.Error: interpreter stdout proxy lost"
+        em.Interpreter._wasProxyInstalled = False
+
+    def test_rmw_extension(self):
+        plugins = list_plugins()
+        rmw_plugin = plugins['rmw']
+
+        p = rmw_plugin()
+        self.assertTrue(plugin_load_parser_correctly(rmw_plugin))
+
+        mock_cliargs = {'rmw': ['cyclonedds']}
+        dig = DockerImageGenerator([rmw_plugin()], mock_cliargs, 'ros:rolling')
+        self.assertEqual(dig.build(), 0)
+        self.assertEqual(dig.run(command='dpkg -l ros-rolling-rmw-cyclonedds-cpp'), 0)
+        self.assertIn('-e RMW_IMPLEMENTATION=rmw_cyclonedds_cpp', dig.generate_docker_cmd('', mode='dry-run'))