Allow using file to override metric map

Override the metric map of each datasource as soon as it is created by
the manager. This override comes from a file whose path is provided by
a setting in config file.

Loading at creation time allows the correct datasource be used when
get_backend is called, this allows loading a datasource whose metric
names get updated outside the watcher's codebase.

The function 'load_metric_map' returns empty-dict in any error case.
Also in case the file is empty where safe_load is unable finds any
yaml documents, it will return None. [1]

Some minor refactoring in the test_manager file for readability and
added tests for file load and metric override.

1 - https://pyyaml.org/wiki/PyYAMLDocumentation

Change-Id: I1df16245f4c7dfd34066f3ab0553cd67154faa58
Implements: blueprint file-based-metric-map

watcher/tests/datasources/test_manager.py

@@ -16,44 +16,72 @@
 
 import mock
 
+from mock import MagicMock
+
 from watcher.common import exception
 from watcher.datasources import gnocchi
 from watcher.datasources import manager as ds_manager
+from watcher.datasources import monasca
 from watcher.tests import base
 
 
 class TestDataSourceManager(base.BaseTestCase):
 
+    def _dsm_config(self, **kwargs):
+        dss = ['gnocchi', 'ceilometer', 'monasca']
+        opts = dict(datasources=dss, metric_map_path=None)
+        opts.update(kwargs)
+        return MagicMock(**opts)
+
+    def _dsm(self, **kwargs):
+        opts = dict(config=self._dsm_config(), osc=mock.MagicMock())
+        opts.update(kwargs)
+        return ds_manager.DataSourceManager(**opts)
+
     def test_get_backend(self):
-        manager = ds_manager.DataSourceManager(
-            config=mock.MagicMock(
-                datasources=['gnocchi', 'ceilometer', 'monasca']),
-            osc=mock.MagicMock())
+        manager = self._dsm()
         backend = manager.get_backend(['host_cpu_usage', 'instance_cpu_usage'])
         self.assertEqual(backend, manager.gnocchi)
 
     def test_get_backend_order(self):
-        manager = ds_manager.DataSourceManager(
-            config=mock.MagicMock(
-                datasources=['monasca', 'ceilometer', 'gnocchi']),
-            osc=mock.MagicMock())
+        dss = ['monasca', 'ceilometer', 'gnocchi']
+        dsmcfg = self._dsm_config(datasources=dss)
+        manager = self._dsm(config=dsmcfg)
         backend = manager.get_backend(['host_cpu_usage', 'instance_cpu_usage'])
         self.assertEqual(backend, manager.monasca)
 
     def test_get_backend_wrong_metric(self):
-        manager = ds_manager.DataSourceManager(
-            config=mock.MagicMock(
-                datasources=['gnocchi', 'ceilometer', 'monasca']),
-            osc=mock.MagicMock())
+        manager = self._dsm()
         self.assertRaises(exception.NoSuchMetric, manager.get_backend,
                           ['host_cpu', 'instance_cpu_usage'])
 
     @mock.patch.object(gnocchi, 'GnocchiHelper')
     def test_get_backend_error_datasource(self, m_gnocchi):
         m_gnocchi.side_effect = exception.DataSourceNotAvailable
-        manager = ds_manager.DataSourceManager(
-            config=mock.MagicMock(
-                datasources=['gnocchi', 'ceilometer', 'monasca']),
-            osc=mock.MagicMock())
+        manager = self._dsm()
         backend = manager.get_backend(['host_cpu_usage', 'instance_cpu_usage'])
         self.assertEqual(backend, manager.ceilometer)
+
+    def test_metric_file_path_not_exists(self):
+        manager = self._dsm()
+        expected = ds_manager.DataSourceManager.metric_map
+        actual = manager.metric_map
+        self.assertEqual(expected, actual)
+        self.assertEqual({}, manager.load_metric_map('/nope/nope/nope.yaml'))
+
+    def test_metric_file_metric_override(self):
+        path = 'watcher.datasources.manager.DataSourceManager.load_metric_map'
+        retval = {
+            monasca.MonascaHelper.NAME: {"host_airflow": "host_fnspid"}
+        }
+        with mock.patch(path, return_value=retval):
+            dsmcfg = self._dsm_config(datasources=['monasca'])
+            manager = self._dsm(config=dsmcfg)
+            backend = manager.get_backend(['host_cpu_usage'])
+            self.assertEqual("host_fnspid", backend.METRIC_MAP['host_airflow'])
+
+    def test_metric_file_invalid_ds(self):
+        with mock.patch('yaml.safe_load') as mo:
+            mo.return_value = {"newds": {"metric_one": "i_am_metric_one"}}
+            mgr = self._dsm()
+            self.assertNotIn('newds', mgr.metric_map.keys())