class_docstr: Test ability to marshall download_button protos.
class_docstr_tok: ["Test","ability","to","marshall","download_button","protos","."]
docstr: Test that file url exist in proto.
docstr_tok: ["Test","that","file","url","exist","in","proto","."]
code: def test_url_exist(self):
      """Test that file url exist in proto."""
      st.download_button("the label", data="juststring")
  
      c = self.get_delta_from_queue().new_element.download_button
      self.assertTrue("/media/" in c.url)
  
file_path: streamlit/lib/tests/streamlit/elements/download_button_test.py
imports: from parameterized import parameterized
  import streamlit
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 3 for calling the DownloadButtonTest obj's underlying member method code with example usage: obj.test_url_exist() without return types