code: def test_empty_text():
      # test originally empty text raises an exception
      wc = WordCloud(stopwords=[])
      with pytest.raises(ValueError):
          wc.generate("")
  
      # test empty-after-filtering text raises an exception
      wc = WordCloud(stopwords=["a", "b"])
      with pytest.raises(ValueError):
          wc.generate("a b a")
  
imports: from wordcloud import WordCloud, get_single_color_func, ImageColorGenerator
  import numpy
  import pytest
  from random import Random
  from numpy.testing import assert_array_equal
  from PIL import Image
  import xml.etree.ElementTree
  import matplotlib
label_desc: Use image node_id 6 for calling a global function with example usage: test_empty_text() without return types