code: def test_euler():
      f = np.zeros((16, 16), np.bool_)
      f[4:8, 4:8] = 1
      assert euler(f) == 1
      assert euler(f, 4) == 1
  
      f[6:7, 5:7] = 0
  
      assert euler(f) == 0
      assert euler(f, 4) == 0
  
imports: import numpy
  from mahotas.euler import euler, _euler_lookup4, _euler_lookup8
  import pytest
label_desc: Use image node_id 2 for calling a global function with example usage: test_euler() without return types