code: def test_observe_single_step(self):
      observer = action_metrics.ContinuousActionObserver()
      observer.observe_first(env=_FAKE_ENV, timestep=_TIMESTEP)
      observer.observe(
          env=_FAKE_ENV, timestep=_TIMESTEP, action=np.array([1])
      )
      self.assertEqual(
          {
              "action[0]_max": 1,
              "action[0]_min": 1,
              "action[0]_mean": 1,
              "action[0]_p50": 1,
          },
          observer.get_metrics(),
      )
  
file_path: acme/acme/utils/observers/action_metrics_test.py
imports: from acme import specs
  from acme.testing import fakes
  from acme.utils.observers import action_metrics
  import dm_env
  import numpy
  from absl.testing import absltest
label_desc: Use image node_id 3 for calling the ActionMetricsTest obj's underlying member method code with example usage: obj.test_observe_single_step() without return types