new_contents: import unittest
  import os
  import stat
  import sys
  sys.path.insert(0, os.path.abspath('..'))
  
  import mexe
  from os import remove
  
  
  class TestHelperFunctions(unittest.TestCase):
  
      def test_contains_shebang(self):
          with open("hello.py", 'w+') as f:
              mexe.put_shebang(f)
          with open("hello.py", 'r') as f:
              self.assertTrue(mexe.contains_shebang(f))
          remove("hello.py")
  
      def test_not_contains_shebang(self):
          with open("hello.py", 'w+') as f:
              f.seek(0)
              f.write("some random text")
          with open("hello.py", 'r') as f:
              self.assertFalse(mexe.contains_shebang(f))
          remove("hello.py")
  
      def test_put_shebang(self):
          shebang = "#! /usr/bin/env python\n"
          with open("hello.py", "w+") as f:
              mexe.put_shebang(f)
          with open("hello.py", 'r') as f:
              self.assertEqual(f.readline(), shebang)
          remove("hello.py")
  
      def test_make_exec(self):
          mexe.make_exec("hello.py")
          st = os.stat("hello.py")
          self.assertTrue(bool(st.st_mode | stat.S_IXOTH | stat.S_IXGRP | stat.S_IXUSR))
          remove("hello.py")
  
subject: add basic tests for helper functions