old_contents: import unittest
  
  import sys
  
  from tests.utils import requires_python_version
  
  
  class TestTreeTrace(unittest.TestCase):
      maxDiff = None
  
      @requires_python_version(3.5)
      def test_async_forbidden(self):
          def check(body):
              with self.assertRaises(ValueError):
                  exec("""
  from birdseye.tracer import TreeTracerBase
  @TreeTracerBase()
  async def f(): """ + body)
  
          check('pass')
  
          if sys.version_info >= (3, 6):
              check('yield 1')
  
new_contents: import sys
  import unittest
  
  from tests.utils import requires_python_version
  
  
  class TestTreeTrace(unittest.TestCase):
      maxDiff = None
  
      @requires_python_version(3.5)
      def test_async_forbidden(self):
          from birdseye.tracer import TreeTracerBase
          tracer = TreeTracerBase()
          with self.assertRaises(ValueError):
              exec("""
  @tracer
  async def f(): pass""")
  
          if sys.version_info >= (3, 6):
              with self.assertRaises(ValueError):
                  exec("""
  @tracer
  async def f(): yield 1""")
  
subject: Fix inner exec syntax error in python 2.7