code: @Test public void testWriteTo() throws Exception {
    String s="Message content";
    byte[] bytes=s.getBytes(HTTP.ISO_8859_1);
    StringEntity httpentity=new StringEntity(s);
    HttpEntityWrapper wrapped=new HttpEntityWrapper(httpentity);
    ByteArrayOutputStream out=new ByteArrayOutputStream();
    wrapped.writeTo(out);
    byte[] bytes2=out.toByteArray();
    Assert.assertNotNull(bytes2);
    Assert.assertEquals(bytes.length,bytes2.length);
    for (int i=0; i < bytes.length; i++) {
      Assert.assertEquals(bytes[i],bytes2[i]);
    }
    out=new ByteArrayOutputStream();
    wrapped.writeTo(out);
    bytes2=out.toByteArray();
    Assert.assertNotNull(bytes2);
    Assert.assertEquals(bytes.length,bytes2.length);
    for (int i=0; i < bytes.length; i++) {
      Assert.assertEquals(bytes[i],bytes2[i]);
    }
    try {
      wrapped.writeTo(null);
      Assert.fail("IllegalArgumentException should have been thrown");
    }
   catch (  IllegalArgumentException ex) {
    }
  }
  