text: from tests.base_test import BaseTest
  
  
  class TestValueExpression(BaseTest):
  
      def test_value_expression_no_default(self):
  
          workflow = self.create_workflow('test_value_expression')
  
          workflow_api = self.get_workflow_api(workflow)
          first_task = workflow_api.next_task
          self.complete_form(workflow, first_task, {'value_expression_value': ''})
  
          workflow_api = self.get_workflow_api(workflow)
          second_task = workflow_api.next_task
          self.assertEqual('', second_task.data['value_expression_value'])
          self.assertNotIn('color', second_task.data)
  
  
  
      def test_value_expression_with_default(self):
  
          workflow = self.create_workflow('test_value_expression')
  
          workflow_api = self.get_workflow_api(workflow)
          first_task = workflow_api.next_task
          self.complete_form(workflow, first_task, {'value_expression_value': 'black'})
  
          workflow_api = self.get_workflow_api(workflow)
          second_task = workflow_api.next_task
          self.assertEqual('black', second_task.data['value_expression_value'])
          self.assertIn('color', second_task.data)
          self.assertEqual('black', second_task.data['color'])
  
      def test_validate_task_with_both_default_and_expression(self):
          # This actually fails validation.
          # We are testing the error message is correct.
          self.load_example_data()
          spec_model = self.load_test_spec('default_value_expression')
          rv = self.app.get('/v1.0/workflow-specification/%s/validate' % spec_model.id, headers=self.logged_in_headers())
          self.assertEqual('default value and value_expression', rv.json[0]['code'])
          self.assertIn('Task_GetName', rv.json[0]['message'])
  