code: def test_stack_negative():
      data = data1.copy()
      _loc = data.columns.get_loc
      data.iloc[0, _loc("y")] *= -1
      data.iloc[len(data) - 1, _loc("y")] *= -1
      p = (
          ggplot(data)
          + geom_col(
              aes("factor(x)", "y", fill="factor(y)"), position="stack"
          )
          + geom_text(
              aes("factor(x)", "y", label="y"),
              position=position_stack(vjust=0.5),
          )
      )
  
      assert p == "stack-negative"
  
imports: import string
  import numpy
  import pandas
  import pytest
  from plotnine import aes, after_stat, geom_bar, geom_boxplot, geom_col, geom_jitter, geom_point, geom_rect, geom_segment, geom_text, ggplot, position_dodge, position_dodge2, position_jitter, position_jitterdodge, position_nudge, position_stack, scale_y_log10, stage
  from plotnine.exceptions import PlotnineError
  from plotnine.positions.position import position
label_desc: Use image node_id 4 for calling a global function with example usage: test_stack_negative() without return types