class_docstr: Tests the Reaction split transformer for the source/target splitting and
  for the reagent mixing operation.
docstr: Tests the reagent - reactant mixing toggle.
docstr_tok: ["Tests","the","reagent","-","reactant","mixing","toggle","."]
code: def test_mixing(self):
      """Tests the reagent - reactant mixing toggle."""
  
      trans = RxnSplitTransformer(sep_reagent=False)
      split_reactions = trans.transform_array(
          X=reactions, y=np.array([]), w=np.array([]), ids=np.array([])
      )
      assert split_reactions[0].shape == (2, 2)
      assert (split_reactions[0] == sep).all()
  
imports: import unittest
  import numpy
  from deepchem.trans.transformers import RxnSplitTransformer
label_desc: Use image node_id 2 for calling the TestRxnSplitTransformer obj's underlying member method code with example usage: obj.test_mixing() without return types