docstr: Tests that `Diff` throws error during `fit` if `component_mask` is specified
  when `dropna = True`; can't allow this since undifferenced components will be different
  length to differenced components.
docstr_tok: ["Tests","that","`","Diff","`","throws","error","during","`","fit","`","if","`","component_mask","`","is","specified","when","`","dropna","=","True","`",";","ca","n't","allow","this","since","undifferenced","components","will","be","different","length","to","differenced","components","."]
code: def test_diff_dropna_and_component_mask_specified(self):
      """
      Tests that `Diff` throws error during `fit` if `component_mask` is specified
      when `dropna = True`; can't allow this since undifferenced components will be different
      length to differenced components.
      """
      diff = Diff(lags=1, dropna=True)
      with pytest.raises(ValueError) as e:
          diff.fit(
              self.sine_series,
              component_mask=np.array([1, 0, 1], dtype=bool),
          )
      assert (
          "Cannot specify `component_mask` with `dropna = True`, "
          "since differenced and undifferenced components will be "
          "of different lengths."
      ) == str(e.value)
  
imports: from copy import deepcopy
  from typing import Optional, Sequence
  import numpy
  import pandas
  import pytest
  from darts.dataprocessing.transformers import Diff
  from darts.timeseries import TimeSeries
  from darts.timeseries import concatenate
  from darts.utils.timeseries_generation import linear_timeseries, sine_timeseries
label_desc: Use image node_id 6 for calling the TestDiff obj's underlying member method code with example usage: obj.test_diff_dropna_and_component_mask_specified() without return types