old_contents: s = "taintedString"
  
  if s.startswith("tainted"):  # $checks=s $branch=true
      pass
  
new_contents: s = "taintedString"
  
  if s.startswith("tainted"):  # $checks=s $branch=true
      pass
  
  sw = s.startswith  # $f-:checks=s $f-:branch=true
  if sw("safe"):
      pass
  
subject: Test false negative from review