Test Slack messages starting with links

Author: r3m0t

tests/backend_tests/slack_tests.py

@@ -247,6 +247,10 @@ def test_slack_markdown_link_preprocessor(self):
             "This is <http://example.com/|a link> and a manual URL: https://example.com/.",
             convert("This is [a link](http://example.com/) and a manual URL: https://example.com/.")
         )
+        self.assertEqual(
+            "<http://example.com/|This is a link>",
+            convert("[This is a link](http://example.com/)")
+        )
         self.assertEqual(
             "This is http://example.com/image.png.",
             convert("This is ![an image](http://example.com/image.png).")