code: def test_observe_first(self):
      observer = measurement_metrics.MeasurementObserver()
      observer.observe_first(env=_FAKE_ENV, timestep=_TIMESTEP)
      self.assertEqual({}, observer.get_metrics())
  
file_path: acme/acme/utils/observers/measurement_metrics_test.py
imports: import copy
  from unittest import mock
  from acme import specs
  from acme.testing import fakes
  from acme.utils.observers import measurement_metrics
  import dm_env
  import numpy
  from absl.testing import absltest
label_desc: Use image node_id 2 for calling the MeasurementMetricsTest obj's underlying member method code with example usage: obj.test_observe_first() without return types