code: def test_set_plot_theme_from_env():
      os.environ["PYVISTA_PLOT_THEME"] = "not a valid theme"
      try:
          with pytest.warns(UserWarning, match="Invalid"):
              _set_plot_theme_from_env()
      finally:
          os.environ.pop("PYVISTA_PLOT_THEME", None)
  
imports: import os
  import pytest
  import vtk
  import pyvista
  from pyvista import colors
  from pyvista.examples.downloads import download_file
  from pyvista.plotting.themes import DarkTheme, Theme, _set_plot_theme_from_env
  from pyvista.plotting.utilities.gl_checks import uses_egl
label_desc: Use image node_id 55 for calling a global function with example usage: test_set_plot_theme_from_env() without return types