class_docstr: Tests that the Barrier gate is correct.
class_docstr_tok: ["Tests","that","the","Barrier","gate","is","correct","."]
docstr: Test that qml.matrix(op) and op.matrix() both fail.
docstr_tok: ["Test","that","qml.matrix","(","op",")","and","op.matrix","(",")","both","fail","."]
code: def test_qml_matrix_fails(self):
      """Test that qml.matrix(op) and op.matrix() both fail."""
      op = qml.Barrier(0)
      with pytest.raises(qml.operation.MatrixUndefinedError):
          qml.matrix(op)
      with pytest.raises(qml.operation.MatrixUndefinedError):
          op.matrix()
  
imports: import pytest
  import numpy
  from pennylane import Snapshot
  import pennylane
label_desc: Use image node_id 10 for calling the TestBarrier obj's underlying member method code with example usage: obj.test_qml_matrix_fails() without return types