code: def test_add_element_blank():
      # Adding onto a blanked themeable
      theme1 = theme_gray() + theme(axis_line_x=l1)  # not blank
      theme2 = theme1 + theme(axis_line_x=blank)  # blank
      theme3 = theme2 + theme(axis_line_x=l3)  # not blank
      theme4 = theme_gray() + theme(axis_line_x=l3)  # for comparison
      assert theme3 != theme1
      assert theme3 != theme2
      assert theme3 == theme4
  
imports: import os
  import pytest
  from plotnine import aes, element_blank, element_line, element_text, facet_grid, facet_wrap, geom_blank, geom_point, ggplot, labs, theme, theme_538, theme_bw, theme_classic, theme_dark, theme_gray, theme_light, theme_linedraw, theme_matplotlib, theme_minimal, theme_seaborn, theme_tufte, theme_void, theme_xkcd
  from plotnine.data import mtcars
label_desc: Use image node_id 6 for calling a global function with example usage: test_add_element_blank() without return types