message: Add test that uses real file in streaming aead.
diff: @@ -16,6 +16,8 @@ from __future__ import division
  from __future__ import print_function
  import io
  +import os
  +import tempfile
  from absl.testing import absltest
  from tink.proto import aes_ctr_hmac_streaming_pb2
  @@ -127,6 +129,28 @@ class StreamingAeadKeyManagerTest(absltest.TestCase):
  with saead_primitive.new_decrypting_stream(ct_source, aad) as ds:
  self.assertEqual(ds.read(), plaintext)
  + def test_encrypt_decrypt_tempfile(self):
  + saead_primitive = self.key_manager_ctr.primitive(
  + self.key_manager_ctr.new_key_data(
  + streaming_aead.streaming_aead_key_templates
  + .AES128_CTR_HMAC_SHA256_4KB))
  + plaintext = b'plaintext'
  + aad = b'associated_data'
  +
  + ciphertext_dest = tempfile.NamedTemporaryFile('wb', delete=False)
  + encryptedfile_name = ciphertext_dest.name
  + with saead_primitive.new_encrypting_stream(ciphertext_dest, aad) as es:
  + n = es.write(plaintext)
  + self.assertTrue(ciphertext_dest.closed)
  + self.assertLen(plaintext, n)
  +
  + ciphertext_src = open(encryptedfile_name, 'rb')
  + with saead_primitive.new_decrypting_stream(ciphertext_src, aad) as ds:
  + output = ds.read()
  + self.assertTrue(ciphertext_src.closed)
  + os.unlink(encryptedfile_name)
  + self.assertEqual(output, plaintext)
  +
  def test_encrypt_decrypt_wrong_aad(self):
  saead_primitive = self.key_manager_ctr.primitive(
  self.key_manager_ctr.new_key_data(
  