code: def test_estimate_tokens(self):
      request = Request(
          prompt=TestOpenAITokenCostEstimator.TEST_PROMPT,
          num_completions=3,
          max_tokens=100,
      )
  
      # Prompt + max number of tokens from completions = 51 + 3 * 100
      assert (
          self._token_cost_estimator.estimate_tokens(
              request, self._mock_metric_service
          )
          == 51 + 3 * 100
      )
  
file_path: H2O/h2o_hf/helm/src/helm/benchmark/metrics/tokens/test_openai_token_cost_estimator.py
imports: from unittest.mock import MagicMock
  from transformers import GPT2TokenizerFast
  from helm.benchmark.metrics.metric_service import MetricService
  from helm.common.authentication import Authentication
  from helm.common.request import Request
  from helm.common.tokenization_request import TokenizationRequestResult, TokenizationToken
  from helm.proxy.services.remote_service import RemoteService
  from .openai_token_cost_estimator import OpenAITokenCostEstimator
label_desc: Use image node_id 2 for calling the TestOpenAITokenCostEstimator obj's underlying member method code with example usage: obj.test_estimate_tokens() without return types