code: def test_get_uid_existing_prefix(self):
      prefix = "existing_prefix"
      naming.get_uid(prefix)
      uid = naming.get_uid(prefix)
      self.assertEqual(uid, 2)
  
imports: from keras.testing import test_case
  from keras.utils import naming
label_desc: Use image node_id 6 for calling the NamingUtilsTest obj's underlying member method code with example usage: obj.test_get_uid_existing_prefix() without return types