code: def test_add_node_with_empty_label(self):
      program = lp_program.Program("foo")
      with self.assertRaisesRegexp(
          ValueError, "Label should not be empty."
      ):
          program.add_node(mock.Mock(autospec=base.Node), label="")
  
file_path: launchpad/launchpad/program_test.py
imports: from unittest import mock
  from absl.testing import absltest
  from launchpad import program
  from launchpad.nodes import base
label_desc: Use image node_id 4 for calling the ProgramTest obj's underlying member method code with example usage: obj.test_add_node_with_empty_label() without return types