text: import unittest
  from test import support
  
  import io # C implementation.
  import _pyio as pyio # Python implementation.
  
  # Simple test to ensure that optimizations in the IO library deliver the
  # expected results.  For best testing, run this under a debug-build Python too
  # (to exercise asserts in the C code).
  
  lengths = list(range(1, 257)) + [512, 1000, 1024, 2048, 4096, 8192, 10000,
                                   16384, 32768, 65536, 1000000]
  
  class BufferSizeTest:
      def try_one(self, s):
          # Write s + "\n" + s to file, then open it and ensure that successive
          # .readline()s deliver what we wrote.
  
          # Ensure we can open TESTFN for writing.
          support.unlink(support.TESTFN)
  
          # Since C doesn't guarantee we can write/read arbitrary bytes in text
          # files, use binary mode.
          f = self.open(support.TESTFN, "wb")
          try:
              # write once with \n and once without
              f.write(s)
              f.write(b"\n")
              f.write(s)
              f.close()
              f = open(support.TESTFN, "rb")
              line = f.readline()
              self.assertEqual(line, s + b"\n")
              line = f.readline()
              self.assertEqual(line, s)
              line = f.readline()
              self.assertFalse(line) # Must be at EOF
              f.close()
          finally:
              support.unlink(support.TESTFN)
  
      def drive_one(self, pattern):
          for length in lengths:
              # Repeat string 'pattern' as often as needed to reach total length
              # 'length'.  Then call try_one with that string, a string one larger
              # than that, and a string one smaller than that.  Try this with all
              # small sizes and various powers of 2, so we exercise all likely
              # stdio buffer sizes, and "off by one" errors on both sides.
              q, r = divmod(length, len(pattern))
              teststring = pattern * q + pattern[:r]
              self.assertEqual(len(teststring), length)
              self.try_one(teststring)
              self.try_one(teststring + b"x")
              self.try_one(teststring[:-1])
  
      def test_primepat(self):
          # A pattern with prime length, to avoid simple relationships with
          # stdio buffer sizes.
          self.drive_one(b"1234567890\00\01\02\03\04\05\06")
  
      def test_nullpat(self):
          self.drive_one(bytes(1000))
  
  
  class CBufferSizeTest(BufferSizeTest, unittest.TestCase):
      open = io.open
  
  class PyBufferSizeTest(BufferSizeTest, unittest.TestCase):
      open = staticmethod(pyio.open)
  
  
  if __name__ == "__main__":
      unittest.main()
  