HashingOutputStream out = new HashingOutputStream(Hashing.md5(), buffer);

    out.write(buf);

    assertEquals(expectedHash, out.hash());
  }

  public void testChecksForNull() throws Exception {
    NullPointerTester tester = new NullPointerTester();
    tester.testAllPublicInstanceMethods(
        new HashingOutputStream(Hashing.md5(), new ByteArrayOutputStream()));