@Test
public void testAddHeaders() {

    String headerName1 = "customized_header1";
    String headerValue1 = "customized_value1";
    String headerName2 = "customized_header2";
    String headerValue2 = "customized_value2";
    HashMap<String, String> headersToAdd = new HashMap<>();
    headersToAdd.put(headerName1, headerValue1);
    headersToAdd.put(headerName2, headerValue2);
    httpService.addHeaders(headersToAdd);
    assertTrue(httpService.getHeaders().get(headerName1).equals(headerValue1));
    assertTrue(httpService.getHeaders().get(headerName2).equals(headerValue2));
}