code: @Test public void testWriteTo() throws Exception {
    File tmpfile=File.createTempFile("testfile",".txt");
    tmpfile.deleteOnExit();
    FileOutputStream outstream=new FileOutputStream(tmpfile);
    outstream.write(0);
    outstream.write(1);
    outstream.write(2);
    outstream.write(3);
    outstream.close();
    FileEntity httpentity=new FileEntity(tmpfile,ContentType.create("text/plain",HTTP.ISO_8859_1));
    ByteArrayOutputStream out=new ByteArrayOutputStream();
    httpentity.writeTo(out);
    byte[] bytes=out.toByteArray();
    Assert.assertNotNull(bytes);
    Assert.assertEquals(tmpfile.length(),bytes.length);
    for (int i=0; i < 4; i++) {
      Assert.assertEquals(i,bytes[i]);
    }
    if (!tmpfile.delete()) {
      Assert.fail("Failed to delete: " + tmpfile);
    }
    try {
      httpentity.writeTo(null);
      Assert.fail("IllegalArgumentException should have been thrown");
    }
   catch (  IllegalArgumentException ex) {
    }
  }
  