code: def test_float16():
      dtype = np.float16
      St = S.astype(dtype)
      Mt = M.astype(int)
      with pytest.raises(TypeError):
          mh.cwatershed(2 - St, Mt)
  
file_path: mahotas/mahotas/tests/test_watershed.py
imports: import numpy
  import mahotas
  import mahotas
  import sys
  import pytest
label_desc: Use image node_id 2 for calling a global function with example usage: test_float16() without return types