register Hostname plugin and add basic tests (#229)

setup.py

@@ -50,6 +50,7 @@
             'git = rocker.git_extension:Git',
             'group_add = rocker.extensions:GroupAdd',
             'home = rocker.extensions:HomeDir',
+            'hostname = rocker.extensions:Hostname',
             'name = rocker.extensions:Name',
             'network = rocker.extensions:Network',
             'nvidia = rocker.nvidia_extension:Nvidia',

test/test_extension.py

@@ -243,6 +243,37 @@ def test_name_extension(self):
         args = p.get_docker_args(mock_cliargs)
         self.assertTrue('--name docker_name' in args)
 
+class HostnameExtensionTest(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_name_extension(self):
+        plugins = list_plugins()
+        name_plugin = plugins['hostname']
+        self.assertEqual(name_plugin.get_name(), 'hostname')
+
+        p = name_plugin()
+        self.assertTrue(plugin_load_parser_correctly(name_plugin))
+
+        mock_cliargs = {'hostname': 'none'}
+        self.assertEqual(p.get_snippet(mock_cliargs), '')
+        self.assertEqual(p.get_preamble(mock_cliargs), '')
+        args = p.get_docker_args(mock_cliargs)
+        self.assertTrue('--hostname none' in args)
+
+        mock_cliargs = {'hostname': 'docker-hostname'}
+        args = p.get_docker_args(mock_cliargs)
+        self.assertTrue('--hostname docker-hostname' in args)
+
 
 class PrivilegedExtensionTest(unittest.TestCase):