Add a test case for load_config

This is just a basic test to make sure loading from file works.

Change-Id: I074f36023ac4198c436fcee1668d32f9d1f0e61b

tests/test_set_config.py

+# 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.
+
+import imp
+import json
+import mock
+import os.path
+import sys
+
+from oslotest import base
+
+# nasty: to import set_config (not a part of the kolla package)
+this_dir = os.path.dirname(sys.modules[__name__].__file__)
+set_configs_file = os.path.abspath(
+    os.path.join(this_dir, '..',
+                 'docker', 'base', 'set_configs.py'))
+
+set_configs = imp.load_source('set_configs', set_configs_file)
+
+
+class LoadFromFile(base.BaseTestCase):
+
+    def test_load_ok(self):
+        in_config = json.dumps({'command': '/bin/true',
+                                'config_files': {}})
+
+        mo = mock.mock_open(read_data=in_config)
+        with mock.patch.object(set_configs, 'open', mo):
+            set_configs.load_config()
+            self.assertEqual([
+                mock.call('/var/lib/kolla/config_files/config.json'),
+                mock.call().__enter__(),
+                mock.call().read(),
+                mock.call().__exit__(None, None, None),
+                mock.call('/run_command', 'w+'),
+                mock.call().__enter__(),
+                mock.call().write(u'/bin/true'),
+                mock.call().__exit__(None, None, None)], mo.mock_calls)