Resolves error response on successful Slack post (#196)

apprise/plugins/NotifySlack.py

@@ -525,6 +525,8 @@ class NotifySlack(NotifyBase):
                     'Response Details:\r\n{}'.format(r.content))
                 return False
 
+            elif attach:
+                # Attachment posts return a JSON string
                 try:
                     response = loads(r.content)
 
@@ -544,6 +546,8 @@ class NotifySlack(NotifyBase):
                     self.logger.debug(
                         'Response Details:\r\n{}'.format(r.content))
                     return False
+            else:
+                response = r.content
 
             # Message Post Response looks like this:
             # {

test/test_slack_plugin.py

@@ -116,7 +116,7 @@ def test_slack_oauth_access_token(mock_post):
     request.content = '{'
 
     # As a result, we'll fail to send our notification
-    assert obj.send(body="test") is False
+    assert obj.send(body="test", attach=attach) is False
 
     request.content = dumps({
         'ok': False,
@@ -125,7 +125,7 @@ def test_slack_oauth_access_token(mock_post):
 
     # A response from Slack (even with a 200 response) still
     # results in a failure:
-    assert obj.send(body="test") is False
+    assert obj.send(body="test", attach=attach) is False
 
     # Handle exceptions reading our attachment from disk (should it happen)
     mock_post.side_effect = OSError("Attachment Error")