new_contents: from __future__ import absolute_import, division, print_function
  
  import numpy as np
  import pandas as pd
  
  from .. import ggplot, aes, geom_density
  from .conftest import cleanup
  
  n = 6  # Some even number greater than 2
  
  # ladder: 0 1 times, 1 2 times, 2 3 times, ...
  df = pd.DataFrame({'x': np.repeat(range(n+1), range(n+1)),
                     'z': np.repeat(range(n//2), range(3, n*2, 4))})
  
  
  @cleanup
  def test_basic():
      p = ggplot(df, aes('x', fill='factor(z)'))
  
      p1 = p + geom_density(kernel='gaussian', alpha=.3)
      p2 = p + geom_density(kernel='gaussian', alpha=.3, trim=True)
      p3 = p + geom_density(kernel='triangular', alpha=.3)  # other
  
      assert p1 == 'gaussian'
      assert p2 == 'gaussian-trimmed'
      assert p3 == 'triangular'
  
subject: Add geom_density tests