code: def test_estimate_tokens(self):
      request = Request(
          prompt="The Center for Research on Foundation Models (CRFM) is "
          "an interdisciplinary initiative born out of the Stanford "
          "Institute for Human-Centered Artificial Intelligence (HAI) "
          "that aims to make fundamental advances in the study, development, "
          "and deployment of foundation models.",
          num_completions=3,
          max_tokens=100,
      )
  
      # AI21 doesn't count tokens from the prompt.
      # So, just count the maximum number of tokens from completions = 3 * 100
      assert (
          self._token_cost_estimator.estimate_tokens(request, Mock())
          == 3 * 100
      )
  
imports: from unittest.mock import Mock
  from helm.common.request import Request
  from .ai21_token_cost_estimator import AI21TokenCostEstimator
label_desc: Use image node_id 2 for calling the TestAI21TokenCostEstimator obj's underlying member method code with example usage: obj.test_estimate_tokens() without return types