Added prefix filtering to TagLine.tags() and Message.tags_from_file()

tests/test_message.py

@@ -543,7 +543,7 @@ class TagsFromFileTestCase(CmmTestCase):
         self.file_txt = tempfile.NamedTemporaryFile(delete=False, suffix='.txt')
         self.file_path_txt = pathlib.Path(self.file_txt.name)
         with open(self.file_path_txt, "w") as fd:
-            fd.write(f"""{TagLine.prefix} tag1 tag2
+            fd.write(f"""{TagLine.prefix} tag1 tag2 ptag3
 {Question.txt_header}
 This is a question.
 {Answer.txt_header}
@@ -560,6 +560,7 @@ This is an answer.
 {Message.tags_yaml_key}:
   - tag1
   - tag2
+  - ptag3
 """)
 
     def tearDown(self) -> None:
@@ -570,11 +571,19 @@ This is an answer.
 
     def test_tags_from_file_txt(self) -> None:
         tags = Message.tags_from_file(self.file_path_txt)
-        self.assertSetEqual(tags, {Tag('tag1'), Tag('tag2')})
+        self.assertSetEqual(tags, {Tag('tag1'), Tag('tag2'), Tag('ptag3')})
 
     def test_tags_from_file_yaml(self) -> None:
         tags = Message.tags_from_file(self.file_path_yaml)
-        self.assertSetEqual(tags, {Tag('tag1'), Tag('tag2')})
+        self.assertSetEqual(tags, {Tag('tag1'), Tag('tag2'), Tag('ptag3')})
+
+    def test_tags_from_file_txt_prefix(self) -> None:
+        tags = Message.tags_from_file(self.file_path_txt, prefix='p')
+        self.assertSetEqual(tags, {Tag('ptag3')})
+
+    def test_tags_from_file_yaml_prefix(self) -> None:
+        tags = Message.tags_from_file(self.file_path_yaml, prefix='p')
+        self.assertSetEqual(tags, {Tag('ptag3')})
 
 
 class MessageIDTestCase(CmmTestCase):