code: def test_format_missing_values():
      data = pd.DataFrame(
          {
              "x": [1, 2, 3, 4],
              "y": [1, 2, 3, 4],
              "c1": [1.1, 2.2, None, 4],
              "c2": ["1.1", "2.2", None, (4, 0)],
          }
      )
      p = (
          ggplot(data, aes("x", "y"))
          + geom_point()
          + geom_text(
              aes(label="c1"),
              nudge_y=0.03,
              va="bottom",
              color="blue",
              format_string="{}",
          )
          + geom_text(
              aes(label="c2"),
              nudge_y=-0.03,
              va="top",
              color="red",
              format_string="{!r}",
          )
      )
      with pytest.warns(PlotnineWarning):
          assert p == "format_missing_values"
  
file_path: plotnine/tests/test_geom_text_label.py
imports: import os
  import numpy
  import pandas
  import pytest
  from plotnine import aes, geom_label, geom_point, geom_text, ggplot, scale_size_continuous, scale_y_continuous
  from plotnine.data import mtcars
  from plotnine.exceptions import PlotnineWarning
label_desc: Use image node_id 6 for calling a global function with example usage: test_format_missing_values() without return types