public void addHeaders(Map<String, String> headersToAdd) {
        headers.putAll(headersToAdd);
    }
@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));
    }