diff --git a/tests/test_main.py b/tests/test_main.py
index db5fcdb..33b9d78 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -7,6 +7,7 @@ from chatmastermind.main import create_parser, ask_cmd
 from chatmastermind.api_client import ai
 from chatmastermind.configuration import Config
 from chatmastermind.storage import create_chat_hist, save_answers, dump_data
+from chatmastermind.tags import Tag, TagLine, TagError
 from unittest import mock
 from unittest.mock import patch, MagicMock, Mock, ANY
 
@@ -231,3 +232,63 @@ class TestCreateParser(CmmTestCase):
             mock_cmdparser.add_parser.assert_any_call('config', help=ANY, aliases=ANY)
             mock_cmdparser.add_parser.assert_any_call('print', help=ANY, aliases=ANY)
             self.assertTrue('.config.yaml' in parser.get_default('config'))
+
+
+class TestTag(CmmTestCase):
+    def test_valid_tag(self) -> None:
+        tag = Tag('mytag')
+        self.assertEqual(tag, 'mytag')
+
+    def test_invalid_tag(self) -> None:
+        with self.assertRaises(TypeError):
+            Tag('tag with space')
+
+    def test_default_separator(self) -> None:
+        self.assertEqual(Tag.default_separator, ' ')
+
+    def test_alternative_separators(self) -> None:
+        self.assertEqual(Tag.alternative_separators, [','])
+
+
+class TestTagLine(CmmTestCase):
+    def test_valid_tagline(self) -> None:
+        tagline = TagLine('TAGS: tag1 tag2')
+        self.assertEqual(tagline, 'TAGS: tag1 tag2')
+
+    def test_invalid_tagline(self) -> None:
+        with self.assertRaises(TagError):
+            TagLine('tag1 tag2')
+
+    def test_prefix(self) -> None:
+        self.assertEqual(TagLine.prefix, 'TAGS:')
+
+    def test_from_set(self) -> None:
+        tags = {Tag('tag1'), Tag('tag2')}
+        tagline = TagLine.from_set(tags)
+        self.assertEqual(tagline, 'TAGS: tag1 tag2')
+
+    def test_tags(self) -> None:
+        tagline = TagLine('TAGS: tag1 tag2')
+        tags = tagline.tags()
+        self.assertEqual(tags, {Tag('tag1'), Tag('tag2')})
+
+    def test_merge(self) -> None:
+        tagline1 = TagLine('TAGS: tag1 tag2')
+        tagline2 = TagLine('TAGS: tag2 tag3')
+        merged_tagline = tagline1.merge({tagline2})
+        self.assertEqual(merged_tagline, 'TAGS: tag1 tag2 tag3')
+
+    def test_delete_tags(self) -> None:
+        tagline = TagLine('TAGS: tag1 tag2 tag3')
+        new_tagline = tagline.delete_tags({Tag('tag1'), Tag('tag3')})
+        self.assertEqual(new_tagline, 'TAGS: tag2')
+
+    def test_add_tags(self) -> None:
+        tagline = TagLine('TAGS: tag1')
+        new_tagline = tagline.add_tags({Tag('tag2'), Tag('tag3')})
+        self.assertEqual(new_tagline, 'TAGS: tag1 tag2 tag3')
+
+    def test_rename_tags(self) -> None:
+        tagline = TagLine('TAGS: old1 old2')
+        new_tagline = tagline.rename_tags({(Tag('old1'), Tag('new1')), (Tag('old2'), Tag('new2'))})
+        self.assertEqual(new_tagline, 'TAGS: new1 new2')