updates the implementation of the slack backend for notifications

Use the slack_sdk instead of the deprecated slackclient. Because according to the official documentation:
>  The slackclient PyPI project is in maintenance mode now and slack-sdk project is the successor.
With this commit one UPGRADE BLOCKER from requirements/requirements.in is removed. Als the license for slack_sdk
is updated and unit tests for slack notifications backend are added.

Signed-off-by: Daniel Ziegenberg <daniel@ziegenberg.at>

awx/main/notifications/slack_backend.py

@@ -2,7 +2,8 @@
 # All Rights Reserved.
 
 import logging
-from slackclient import SlackClient
+from slack_sdk import WebClient
+from slack_sdk.errors import SlackApiError
 
 from django.utils.encoding import smart_text
 from django.utils.translation import ugettext_lazy as _
@@ -28,7 +29,7 @@ class SlackBackend(AWXBaseEmailBackend, CustomNotificationBase):
             self.color = hex_color
 
     def send_messages(self, messages):
-        connection = SlackClient(self.token)
+        client = WebClient(self.token)
         sent_messages = 0
         for m in messages:
             try:
@@ -36,15 +37,15 @@ class SlackBackend(AWXBaseEmailBackend, CustomNotificationBase):
                     if r.startswith('#'):
                         r = r[1:]
                     if self.color:
-                        ret = connection.api_call("chat.postMessage", channel=r, as_user=True, attachments=[{"color": self.color, "text": m.subject}])
+                        response = client.chat_postMessage(channel=r, as_user=True, attachments=[{"color": self.color, "text": m.subject}])
                     else:
-                        ret = connection.api_call("chat.postMessage", channel=r, as_user=True, text=m.subject)
-                    logger.debug(ret)
-                    if ret['ok']:
+                        response = client.chat_postMessage(channel=r, as_user=True, text=m.subject)
+                    logger.debug(response)
+                    if response['ok']:
                         sent_messages += 1
                     else:
-                        raise RuntimeError("Slack Notification unable to send {}: {} ({})".format(r, m.subject, ret['error']))
-            except Exception as e:
+                        raise RuntimeError("Slack Notification unable to send {}: {} ({})".format(r, m.subject, response['error']))
+            except SlackApiError as e:
                 logger.error(smart_text(_("Exception sending messages: {}").format(e)))
                 if not self.fail_silently:
                     raise

awx/main/tests/unit/notifications/test_slack.py

@@ -0,0 +1,73 @@
+import pytest
+
+from unittest import mock
+from django.core.mail.message import EmailMessage
+
+import awx.main.notifications.slack_backend as slack_backend
+
+
+def test_send_messages():
+    with mock.patch('awx.main.notifications.slack_backend.WebClient') as slack_sdk_mock:
+        WebClient_mock = slack_sdk_mock.return_value
+        WebClient_mock.chat_postMessage.return_value = {'ok': True}
+        backend = slack_backend.SlackBackend('slack_access_token')
+        message = EmailMessage(
+            'test subject',
+            'test body',
+            [],
+            [
+                '#random',
+            ],
+        )
+        sent_messages = backend.send_messages(
+            [
+                message,
+            ]
+        )
+        WebClient_mock.chat_postMessage.assert_called_once_with(channel='random', as_user=True, text='test subject')
+        assert sent_messages == 1
+
+
+def test_send_messages_with_color():
+    with mock.patch('awx.main.notifications.slack_backend.WebClient') as slack_sdk_mock:
+        WebClient_mock = slack_sdk_mock.return_value
+        WebClient_mock.chat_postMessage.return_value = {'ok': True}
+        backend = slack_backend.SlackBackend('slack_access_token', hex_color='#006699')
+        message = EmailMessage(
+            'test subject',
+            'test body',
+            [],
+            [
+                '#random',
+            ],
+        )
+        sent_messages = backend.send_messages(
+            [
+                message,
+            ]
+        )
+
+        WebClient_mock.chat_postMessage.assert_called_once_with(channel='random', as_user=True, attachments=[{'color': '#006699', 'text': 'test subject'}])
+        assert sent_messages == 1
+
+
+def test_send_messages_fail():
+    with mock.patch('awx.main.notifications.slack_backend.WebClient') as slack_sdk_mock, pytest.raises(RuntimeError, match=r'.*not_in_channel.*'):
+        WebClient_mock = slack_sdk_mock.return_value
+        WebClient_mock.chat_postMessage.return_value = {'ok': False, 'error': 'not_in_channel'}
+        backend = slack_backend.SlackBackend('slack_access_token')
+        message = EmailMessage(
+            'test subject',
+            'test body',
+            [],
+            [
+                '#not_existing',
+            ],
+        )
+        sent_messages = backend.send_messages(
+            [
+                message,
+            ]
+        )
+        WebClient_mock.chat_postMessage.assert_called_once_with(channel='not_existing', as_user=True, text='test subject')
+        assert sent_messages == 0