public void addHeader(String key, String value) {
        headers.put(key, value);
    }
@Test
    public void testAddHeader() {
        String headerName = "customized_header0";
        String headerValue = "customized_value0";
        httpService.addHeader(headerName, headerValue);
        assertTrue(httpService.getHeaders().get(headerName).equals(headerValue));
    }