old_contents: import py
  import subprocess
  import sys
  import pytest
  import _pytest
  
  MODSET = [
      x for x in py.path.local(_pytest.__file__).dirpath().visit('*.py')
      if x.purebasename != '__init__'
  ]
  
  
  @pytest.mark.parametrize('modfile', MODSET, ids=lambda x: x.purebasename)
  def test_fileimport(modfile):
      res = subprocess.call([
          sys.executable,
          '-c', 'import sys, py; py.path.local(sys.argv[1]).pyimport()',
          modfile.strpath,
      ])
      if res:
          pytest.fail("command result %s" % res)
  
new_contents: import py
  import subprocess
  import sys
  import pytest
  import _pytest
  
  MODSET = [
      x for x in py.path.local(_pytest.__file__).dirpath().visit('*.py')
      if x.purebasename != '__init__'
  ]
  
  
  @pytest.mark.parametrize('modfile', MODSET, ids=lambda x: x.purebasename)
  def test_fileimport(modfile):
      # this test ensures all internal packages can import
      # without needing the pytest namespace being set
      # this is critical for the initialization of xdist
  
      res = subprocess.call([
          sys.executable,
          '-c', 'import sys, py; py.path.local(sys.argv[1]).pyimport()',
          modfile.strpath,
      ])
      if res:
          pytest.fail("command result %s" % res)
  
subject: add a comment explaining the modimport tests