code: def test_mu1_tet():
      res1 = pts2mu1_tet([2, 2, 2], [3, 2, 2], [2, 3, 2], [2, 2, 3])
      res2 = pts2mu1_tet([0, 0, 0], [1, 0, 0], [0, 1, 0], [0, 0, 1])
      assert res1 == res2
      assert intvol.mu1_tet(0, 0, 0, 0, 0, 0, 0, 0, 0, 0) == 0
      # This used to generate nan values
      assert intvol.mu1_tet(0, 0, 0, 0, 1, 0, 0, -1, 0, 1) == 0
  
imports: from itertools import combinations
  import numpy
  import numpy.linalg
  import pytest
  from numpy.testing import assert_almost_equal, assert_array_equal
  from ..None import intvol
label_desc: Use image node_id 15 for calling a global function with example usage: test_mu1_tet() without return types