code: def test_to_lower():
      assert helpers.to_lower(None, None, "EPSG:3857") == "epsg:3857"
  
file_path: rasterio/tests/test_rio_helpers.py
imports: import click
  import pytest
  from rasterio.errors import FileOverwriteError
  from rasterio.rio import helpers
label_desc: Use image node_id 10 for calling a global function with example usage: test_to_lower() without return types