text: import vaex
  import numpy as np
  
  
  def test_countna(df_factory):
      x = np.array([5, '', 1, 4, None, 6, np.nan, np.nan, 10, '', 0, 0, -13.5])
      y_data = np.array([np.nan, 2, None, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13])
      y_mask = np.array([0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1])
      y = np.ma.MaskedArray(data=y_data, mask=y_mask)
      df = df_factory(x=x, y=y)
      pandas_df = df.to_pandas_df(array_type='numpy')
  
      assert df.x.countna() == pandas_df.x.isna().sum()
      assert df.y.countna() == pandas_df.y.isna().sum()
      assert df.x.countnan() == 2
      assert df.y.countmissing() == 6
  