code: def test_exacteig():
      from deepchem.utils.differentiation_utils.symeig import exacteig
      from deepchem.utils.differentiation_utils import LinearOperator
  
      torch.manual_seed(100)
      mat = LinearOperator.m(torch.randn(2, 2))
      eival, eivec = exacteig(mat, 2, "lowest", None)
      assert eival.shape == torch.Size([2])
      assert eivec.shape == torch.Size([2, 2])
  
imports: import pytest
label_desc: Use image node_id 27 for calling a global function with example usage: test_exacteig() without return types