code: def testMultStringSingleKey(self):
      p = Pool()
      p.add("foo", "foo")
      p.add("foo", "bar")
  
      YamlOutput(filename="test.yaml")(p)
  
      result = getYaml("test.yaml")
      expected = (
          self.metadata
          + """
  foo: ["foo", "bar"]
  """
      )
  
      self.assertEqual(result, expected)
  
imports: from essentia_test import *
  from essentia._essentia import version
  import os
  import json
label_desc: Use image node_id 4 for calling the TestYamlOutput obj's underlying member method code with example usage: obj.testMultStringSingleKey() without return types