refactor: scope save_file side_effect to dedicated fixture, not shared mock

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: chrisdpurcell

tests/integration/test_main_window.py

@@ -14,17 +14,10 @@
 
 @pytest.fixture
 def mock_file_svc():
-    from src.services.file_service import FileService
-
     svc = MagicMock()
     svc.open_file.return_value = TextDocument(
         filepath="/tmp/test.txt", content="hello world", encoding="utf-8"
     )
-    # Delegate save_file to the real FileService so tests that write files to
-    # tmp_path can verify disk contents. Tests that only check signals are
-    # unaffected because they don't inspect file system state.
-    _real_svc = FileService()
-    svc.save_file.side_effect = _real_svc.save_file
     return svc
 
 
@@ -462,19 +455,33 @@ def test_char_count_updates_on_delete_without_cursor_move(self, window, qtbot):
         assert "8 chars" in window._cursor_label.text()
 
 
+@pytest.fixture
+def _real_save_svc(mock_file_svc):
+    """Extends mock_file_svc with real FileService.save_file for disk-write assertions."""
+    from src.services.file_service import FileService
+    mock_file_svc.save_file.side_effect = FileService().save_file
+    return mock_file_svc
+
+
+@pytest.fixture
+def window_real_save(_real_save_svc, mock_text_svc, qapp):
+    vm = MainViewModel(_real_save_svc, mock_text_svc)
+    return MainWindow(vm)
+
+
 class TestActionSaveAsHandler:
-    def test_chosen_path_is_saved(self, window, tmp_path, monkeypatch, qtbot):
+    def test_chosen_path_is_saved(self, window_real_save, tmp_path, monkeypatch, qtbot):
         """getSaveFileName returns path → file saved to that path."""
         out = tmp_path / "renamed.txt"
         monkeypatch.setattr(
             "src.views.main_window.QFileDialog.getSaveFileName",
             lambda *a, **kw: (str(out), ""),
         )
-        window._plain_text_edit.setPlainText("save-as content")
-        with qtbot.waitSignal(window._viewmodel.file_saved, timeout=2000):
-            window._on_action_save_as()
+        window_real_save._plain_text_edit.setPlainText("save-as content")
+        with qtbot.waitSignal(window_real_save._viewmodel.file_saved, timeout=2000):
+            window_real_save._on_action_save_as()
         assert out.read_text(encoding="utf-8") == "save-as content"
-        assert window._file_name_edit.text() == str(out)
+        assert window_real_save._file_name_edit.text() == str(out)
 
     def test_cancelled_dialog_is_no_op(self, window, monkeypatch):
         """getSaveFileName returns '' → nothing saved."""