code: def test_singleton(self, x, y):
      p = lm._RegressionPlotter(x, y)
      assert not p.fit_reg
  
imports: import warnings
  import numpy
  import matplotlib
  import matplotlib.pyplot
  import pandas
  import pytest
  import numpy.testing
  import pandas.testing
  from seaborn import regression
  from seaborn.palettes import color_palette
label_desc: Use image node_id 6 for calling the TestRegressionPlotter obj's underlying member method code with example usage: obj.test_singleton(x, y) without return types