added 'message_in()' function and test

chatmastermind/message.py

@@ -3,7 +3,7 @@ Module implementing message related functions and classes.
 """
 import pathlib
 import yaml
-from typing import Type, TypeVar, ClassVar, Optional, Any, Union, Final, Literal
+from typing import Type, TypeVar, ClassVar, Optional, Any, Union, Final, Literal, Iterable
 from dataclasses import dataclass, asdict, field
 from .tags import Tag, TagLine, TagError, match_tags
 
@@ -57,6 +57,20 @@ def source_code(text: str, include_delims: bool = False) -> list[str]:
     return code_sections
 
 
+def message_in(message: MessageInst, messages: Iterable[MessageInst]) -> bool:
+    """
+    Searches the given message list for a message with the same file
+    name as the given one (i. e. it compares Message.file_path.name).
+    If the given message has no file_path, False is returned.
+    """
+    if not message.file_path:
+        return False
+    for m in messages:
+        if m.file_path and m.file_path.name == message.file_path.name:
+            return True
+    return False
+
+
 @dataclass(kw_only=True)
 class MessageFilter:
     """