code: def test_should_return_expr_without_table_source(self):
      constant = Batch(pd.DataFrame([1]))
      expression = [
          type(
              "AbstractExpression",
              (),
              {
                  "evaluate": lambda x: constant,
                  "find_all": lambda expr: [],
              },
          )
      ]
  
      plan = type(
          "ProjectPlan",
          (),
          {"predicate": None, "target_list": expression},
      )
      proj_executor = ProjectExecutor(MagicMock(), plan)
  
      actual = list(proj_executor.exec())[0]
      self.assertEqual(constant, actual)
  
imports: import unittest
  import pandas
  from mock import MagicMock
  from evadb.executor.project_executor import ProjectExecutor
  from evadb.models.storage.batch import Batch
label_desc: Use image node_id 1 for calling the ProjectExecutorTest obj's underlying member method code with example usage: obj.test_should_return_expr_without_table_source() without return types