code: def test_track_from_multiple_files(tmp_dir):
      d1 = {"Train": {"us": {"lr": 10}}}
      d2 = {"Train": {"us": {"layers": 100}}}
  
      fs = LocalFileSystem()
      path1 = "params.yaml"
      path2 = "params2.yaml"
      (tmp_dir / path1).dump(d1, fs=fs)
      (tmp_dir / path2).dump(d2, fs=fs)
  
      context = Context.load_from(fs, path1)
      c = Context.load_from(fs, path2)
      context.merge_update(c)
  
      def key_tracked(d, path, key):
          return key in d[relpath(path)]
  
      with context.track() as tracked:
          context.select("Train")
          assert not key_tracked(tracked, path1, "Train")
          assert not key_tracked(tracked, path2, "Train")
  
          context.select("Train.us")
          assert not key_tracked(tracked, path1, "Train.us")
          assert not key_tracked(tracked, path2, "Train.us")
  
          context.select("Train.us.lr")
          assert key_tracked(tracked, path1, "Train.us.lr")
          assert not key_tracked(tracked, path2, "Train.us.lr")
          context.select("Train.us.layers")
          assert not key_tracked(tracked, path1, "Train.us.layers")
          assert key_tracked(tracked, path2, "Train.us.layers")
  
      context = Context.clone(context)
      assert not context._tracked_data
  
      # let's see with an alias
      context["us"] = context["Train"]["us"]
      with context.track() as tracked:
          context.select("us")
          assert not key_tracked(tracked, path1, "Train.us")
          assert not key_tracked(tracked, path2, "Train.us")
  
          context.select("us.lr")
          assert key_tracked(tracked, path1, "Train.us.lr")
          assert not key_tracked(tracked, path2, "Train.us.lr")
          context.select("Train.us.layers")
          assert not key_tracked(tracked, path1, "Train.us.layers")
          assert key_tracked(tracked, path2, "Train.us.layers")
  
imports: from dataclasses import asdict
  from math import pi
  import pytest
  from dvc.fs import LocalFileSystem
  from dvc.parsing import DEFAULT_PARAMS_FILE
  from dvc.parsing.context import Context, CtxDict, CtxList, KeyNotInContext, MergeError, ParamsLoadError, Value, recurse_not_a_node
  from dvc.utils import relpath
  from dvc.utils.serialize import dumps_yaml
label_desc: Use image node_id 15 for calling a global function with example usage: test_track_from_multiple_files(tmp_dir) and returns: unknown