code: def test_scm_track_changed_files(scm_context):
      scm_context.track_changed_files()
      scm_context.scm.add.assert_not_called()
  
      scm_context.track_file("foo")
      scm_context.track_changed_files()
      scm_context.scm.add.assert_called_once_with({"foo"})
  
file_path: dvc/tests/unit/repo/test_scm_context.py
imports: import re
  import pytest
  from dvc.repo.scm_context import SCMContext
  from dvc.scm import Git, NoSCM
label_desc: Use image node_id 4 for calling a global function with example usage: test_scm_track_changed_files(scm_context) without return types