Move structural typing tests into interface unit test files.

Align test layout with the one-test-file-per-interface convention by removing structural_typing_test.py.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/connection_aware_interface_test.py

@@ -7,6 +7,24 @@ from python_repositories.interfaces.connection_aware_interface import (
 )
 
 
+class FakeConnection:
+    """Plain class that satisfies ConnectionAwareInterface without inheritance."""
+
+    def connect(self) -> None:
+        pass
+
+    def disconnect(self) -> None:
+        pass
+
+    def is_connected(self) -> bool:
+        return True
+
+
+def accepts_connection_aware(connection: ConnectionAwareInterface) -> None:
+    """Type-checking hook for ConnectionAwareInterface structural subtyping."""
+    connection.is_connected()
+
+
 def test_instantiation_fails_when_connect_not_implemented() -> None:
     """Test that instantiation fails if connect is not implemented."""
 
@@ -53,3 +71,10 @@ def test_instantiation_fails_when_is_connected_not_implemented() -> None:
 
     with pytest.raises(TypeError):
         _ = Incomplete()  # type: ignore
+
+
+def test_structural_subtyping() -> None:
+    """Test that a plain class satisfies ConnectionAwareInterface structurally."""
+    connection: ConnectionAwareInterface = FakeConnection()
+    accepts_connection_aware(connection)
+    assert isinstance(connection, ConnectionAwareInterface)