code: def test_bar():
      import dtale.views as views
  
      df, _ = views.format_data(
          pd.DataFrame(dict(a=[1, 2, 3, 4, 5, 6]))
      )
      with build_app(url=URL).test_client() as c:
          build_data_inst({c.port: df})
  
          resp = c.get("/dtale/missingno/bar/{}".format(c.port))
          assert resp.content_type == "image/png"
  
file_path: dtale/tests/dtale/test_missingno.py
imports: import pandas
  import pytest
  from dtale.app import build_app
  from tests.dtale.test_views import URL
  from tests.dtale import build_data_inst
label_desc: Use image node_id 2 for calling a global function with example usage: test_bar() without return types