code: def test_setting_built_in_theme_str(self) -> None:
      obj = SomeModel()
      doc = Document()
      doc.add_root(obj)
      doc.theme = DARK_MINIMAL
      assert (
          "#20262B"
          == doc.theme._json["attrs"]["Plot"]["background_fill_color"]
      )
  
imports: from __future__ import annotations
  import pytest
  import os
  import tempfile
  from bokeh.core.properties import Int, String
  from bokeh.core.property_mixins import FillProps, LineProps, TextProps
  from bokeh.document import Document
  from bokeh.model import Model
  from bokeh.plotting import figure
  from bokeh.util.deprecation import BokehDeprecationWarning
  from bokeh.themes import Theme, built_in_themes, DARK_MINIMAL, LIGHT_MINIMAL
label_desc: Use image node_id 19 for calling the TestThemes obj's underlying member method code with example usage: obj.test_setting_built_in_theme_str() without return types