Fix missing mocks for Parser

The tests are not installing Snippy dependencies like the
Parser class because there are no release from Snippy that
contains these. There are temporary mocks that take care
of the Parser class. The mocks were missing for new groups
and tags attribute parsers.

Signed-off-by: Heikki Laaksonen <laaksonen.heikki.j@gmail.com>

tests/conftest.py

@@ -26,10 +26,12 @@
 def mock_snippy(mocker):
     """Mock Snippy."""
 
-    mocker.patch.object(Parser, "format_data", return_value=[])
+    mocker.patch.object(Parser, "format_data", return_value=())
     mocker.patch.object(Parser, "format_brief", return_value="")
     mocker.patch.object(Parser, "format_description", return_value="")
     mocker.patch.object(Parser, "format_name", return_value="")
+    mocker.patch.object(Parser, "format_groups", return_value=())
+    mocker.patch.object(Parser, "format_tags", return_value=())
 
 
 class Const(object):  # pylint: disable=too-few-public-methods
@@ -56,3 +58,11 @@ def format_description(cls, category, value):
     @classmethod
     def format_name(cls, category, value):
         """Dummy method for mock."""
+
+    @classmethod
+    def format_groups(cls, category, value):
+        """Dummy method for mock."""
+
+    @classmethod
+    def format_tags(cls, category, value):
+        """Dummy method for mock."""