code: def test_flatten_unflatten_methods():
      """Test the _flatten and _unflatten methods."""
      feature_vector = [1, 2, 3]
      op = qml.DisplacementEmbedding(
          features=feature_vector, wires=range(3), method="phase", c=0.5
      )
      data, metadata = op._flatten()
      assert op.data == data
  
      # make sure metadata hashable
      assert hash(metadata)
  
      new_op = type(op)._unflatten(*op._flatten())
      assert qml.equal(new_op, op)
      assert new_op is not op
      assert new_op._name == "DisplacementEmbedding"
  
imports: import pytest
  import numpy
  from pennylane import numpy
  import pennylane
label_desc: Use image node_id 2 for calling a global function with example usage: test_flatten_unflatten_methods() without return types