code: @Test public void testWriteTo() throws Exception {
    byte[] bytes="Message content".getBytes(HTTP.ISO_8859_1);
    InputStream instream=new ByteArrayInputStream(bytes);
    InputStreamEntity httpentity=new InputStreamEntity(instream,7);
    ByteArrayOutputStream out=new ByteArrayOutputStream();
    httpentity.writeTo(out);
    byte[] bytes2=out.toByteArray();
    Assert.assertNotNull(bytes2);
    Assert.assertEquals(7,bytes2.length);
    String s=new String(bytes2,HTTP.ISO_8859_1);
    Assert.assertEquals("Message",s);
    instream=new ByteArrayInputStream(bytes);
    httpentity=new InputStreamEntity(instream,20);
    out=new ByteArrayOutputStream();
    httpentity.writeTo(out);
    bytes2=out.toByteArray();
    Assert.assertNotNull(bytes2);
    Assert.assertEquals(bytes.length,bytes2.length);
    instream=new ByteArrayInputStream(bytes);
    httpentity=new InputStreamEntity(instream,-1);
    out=new ByteArrayOutputStream();
    httpentity.writeTo(out);
    bytes2=out.toByteArray();
    Assert.assertNotNull(bytes2);
    Assert.assertEquals(bytes.length,bytes2.length);
    try {
      httpentity.writeTo(null);
      Assert.fail("IllegalArgumentException should have been thrown");
    }
   catch (  IllegalArgumentException ex) {
    }
  }
  