requestHeaders.set("foo", "bar");
TestXhrTransport transport = new TestXhrTransport();
transport.setRequestHeaders(requestHeaders);
transport.sendMessageResponseToReturn = new ResponseEntity<>(HttpStatus.NO_CONTENT);
URI url = new URI("http://example.com");
transport.executeSendRequest(url, new TextMessage("payload"));
assertEquals(2, transport.actualSendRequestHeaders.size());
assertEquals("bar", transport.actualSendRequestHeaders.getFirst("foo"));
assertEquals(MediaType.APPLICATION_JSON, transport.actualSendRequestHeaders.getContentType());
}