old_contents: from polyphony import testbench
  
  def mul_add(a, b, c, d):
      return a * b + c * d
  
  @testbench
  def test():
      assert 17 == mul_add(1, 2, 3, 4)
      assert 62 == mul_add(4, 5, 6, 7)
  
  test()
  
new_contents: from polyphony import testbench
  
  def mul_add(a, b, c, d):
      return a * b + c * d
  
  @testbench
  def test():
      assert 19 == mul_add(1, 2, 3, 4)
      assert 62 == mul_add(4, 5, 6, 7)
  
  test()
  
subject: fix the bug.