code: def test_integrator(self):
      initial_state = self.euclidean.random_point(2)
  
      def function(state, _time):
          _, velocity = state
          return gs.stack([velocity, gs.zeros_like(velocity)])
  
      for step in ["euler", "rk2", "rk4"]:
          flow = integrator.integrate(
              function, initial_state, step=step
          )
          result = flow[-1][0]
          expected = initial_state[0] + initial_state[1]
  
          self.assertAllClose(result, expected)
  
file_path: geomstats/tests/tests_geomstats/test_integrator.py
imports: import pytest
  import geomstats.backend
  import geomstats.integrator
  from geomstats.geometry.euclidean import Euclidean
  from geomstats.geometry.matrices import Matrices
  from geomstats.test.test_case import TestCase
label_desc: Use image node_id 9 for calling the TestIntegrator obj's underlying member method code with example usage: obj.test_integrator() and returns: gs