class_docstr: Test ability to marshall form protos.
class_docstr_tok: ["Test","ability","to","marshall","form","protos","."]
docstr: Test that forms cannot be nested in other forms.
code: def test_form_in_form(self):
      """Test that forms cannot be nested in other forms."""
  
      with self.assertRaises(StreamlitAPIException) as ctx:
          with st.form("foo"):
              with st.form("bar"):
                  pass
  
      self.assertEqual(
          str(ctx.exception), "Forms cannot be nested in other forms."
      )
  
imports: from unittest.mock import MagicMock, patch
  import streamlit
  from streamlit.errors import StreamlitAPIException
  from streamlit.runtime.state.session_state import RegisterWidgetResult
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 5 for calling the FormMarshallingTest obj's underlying member method code with example usage: obj.test_form_in_form() without return types