[ADD] base_external_system: Implement interface/adapter (#993)

* [ADD] base_external_system: Implement interface/adapter for external systems

* base_external_system: Fix OS model, add inherits, add validate

* base_external_system: Usability and private key pass

* base_external_system: Use contextmanager in adapter client

* base_external_system: Move contextmanager to interface

* base_external_system: Include contextmanager on adapter and system

* base_external_system: Unify client

* Use password widget for password field

* Add tests & security

* Fix lint

* Add plaintext note

base_external_system/tests/test_external_system_adapter.py

@@ -0,0 +1,45 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 LasLabs Inc.
+# License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl).
+
+from odoo.exceptions import UserError
+
+from .common import Common
+
+
+class TestExternalSystemAdapter(Common):
+
+    def setUp(self):
+        super(TestExternalSystemAdapter, self).setUp()
+        self.system = self.env.ref('base_external_system.external_system_os')
+        self.record = self.env['external.system.adapter'].new({
+            'system_id': self.system.id,
+        })
+
+    def test_client_yields_client(self):
+        """It should yield the client."""
+        with self._mock_method('external_get_client') as magic:
+            with self.record.client() as client:
+                self.assertEqual(client, magic())
+
+    def test_client_destroys_client(self):
+        """It should destroy the client after use."""
+        with self._mock_method('external_destroy_client') as magic:
+            with self.record.client() as client:
+                self.assertFalse(magic.call_count)
+            magic.assert_called_once_with(client)
+
+    def test_external_get_client_ensure_one(self):
+        """It should assert singletons."""
+        with self.assertRaises(ValueError):
+            self.env['external.system.adapter'].external_get_client()
+
+    def test_external_destroy_client_ensure_one(self):
+        """It should assert singletons."""
+        with self.assertRaises(ValueError):
+            self.env['external.system.adapter'].external_destroy_client(None)
+
+    def test_external_test_connection(self):
+        """It should raise a UserError."""
+        with self.assertRaises(UserError):
+            self.record.external_test_connection()