code: def test_Merge(self) -> None:
      obsd = ObservationData(
          metric_names=["m1", "m2", "m2"],
          means=np.array([1.0, 2.0, 1.0]),
          covariance=np.array(
              [[1.0, 0.2, 0.4], [0.2, 2.0, 0.8], [0.4, 0.8, 3.0]]
          ),
      )
      obsd2 = ivw_metric_merge(obsd)
      self.assertEqual(obsd2.metric_names, ["m1", "m2"])
      self.assertTrue(
          np.array_equal(obsd2.means, np.array([1.0, 0.6 * 2 + 0.4]))
      )
      cov12 = 0.2 * 0.6 + 0.4 * 0.4
      # var(w1*y1 + w2*y2) =
      # w1 ** 2 * var(y1) + w2 ** 2 * var(y2) + 2 * w1 * w2 * cov(y1, y2)
      cov22 = 0.6**2 * 2.0 + 0.4**2 * 3 + 2 * 0.6 * 0.4 * 0.8
      cov_true = np.array([[1.0, cov12], [cov12, cov22]])
      discrep = np.max(np.abs(obsd2.covariance - cov_true))
      self.assertTrue(discrep < 1e-8)
  
file_path: Ax/ax/modelbridge/transforms/tests/test_ivw_transform.py
imports: import numpy
  from ax.core.observation import ObservationData
  from ax.modelbridge.transforms.ivw import IVW, ivw_metric_merge
  from ax.utils.common.testutils import TestCase
label_desc: Use image node_id 2 for calling the IVWTransformTest obj's underlying member method code with example usage: obj.test_Merge() without return types