code: def test_diff_sparse(self):
      # GH#28813 .diff() should work for sparse dataframes as well
      sparse_df = DataFrame([[0, 1], [1, 0]], dtype="Sparse[int]")
  
      result = sparse_df.diff()
      expected = DataFrame(
          [[np.nan, np.nan], [1.0, -1.0]],
          dtype=pd.SparseDtype("float", 0.0),
      )
  
      tm.assert_frame_equal(result, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import DataFrame, Series, Timestamp, date_range
  import pandas._testing
label_desc: Use image node_id 20 for calling the TestDataFrameDiff obj's underlying member method code with example usage: obj.test_diff_sparse() without return types