Junit test case for a restful client using mockito

I have no idea before how to write the test cases, when i saw online tutorials i understand how to write it for a simple method with success and failure scenario. Now i have a method for http get which calls a restful API and returns a json response. I have like 6 parameters to include in the url and get a json response back. Now, my understanding so far is for success scenario here i should just hard code those input parameters and test if i am getting json back and for failure not getting json response back. Is this correct or do i have to do something else?

i mean i have a code something like

public List getStoreLocations(StoreData storeData) { List storeList = null;

try {
    HttpClient httpclient = HttpClientBuilder.create().build();
    StringBuilder urlStrngBuildr = new StringBuilder(
            https://<hostname>/xyz/abc);
    Utility.addParameterToUrl(urlStrngBuildr,
            Utility.APP_NAME,
            Constants.APP_VALUE);
    Utility.addParameterToUrl(urlStrngBuildr,
            Constants.VERSION_PARAM_NAME,
            Constants.VERSION_PARAM_VALUE);
    if (storeData.getCity() != null && storeData.getState() != null) {
        StringBuilder addressParamValue = new StringBuilder(
                storeData.getCity());
        addressParamValue.append(Constants.COMMA);
        addressParamValue.append(storeData.getState());
        Utility.addParameterToUrl(urlStrngBuildr,
                Constants.ADDRESS_PARAM_NAME,
                addressParamValue.toString());
    } else if (storeData.getZip() != null) {
        Utility.addParameterToUrl(urlStrngBuildr,
                Constants.ZIP_PARAM_NAME, storeData.getZip());
    }

    Utility.addParameterToUrl(urlStrngBuildr,
            Constants.PRODUCT_PARAM_NAME,
            storeData.getProduct());
    Utility.addParameterToUrl(urlStrngBuildr,
            Constants.COUNTRY_PARAM_NAME,
            storeData.getCountry());
    Utility.addParameterToUrl(urlStrngBuildr,
            Constants.DISTANCE_PARAM_NAME,
            storeData.getDistance());
    Utility.addParameterToUrl(urlStrngBuildr,
            Constants.SIZE_PARAM_NAME, storeData.getSize());

    HttpGet getRequest = new HttpGet(new java.net.URI(
            urlStrngBuildr.toString()));

    getRequest.addHeader(BasicScheme.authenticate(
            new UsernamePasswordCredentials(username,password),
        Constants.ENCODING_TYPE, false));

    JSONResponseHandler responseHandler = new JSONResponseHandler();
    String json = httpclient.execute(getRequest, responseHandler)
            .toString();

    Gson gson = new Gson();

    StoreResponse response = gson.fromJson(json,
            StoreResponse.class);

    StoreDetails[] strDetails = response.getResult();

    storeDetailsList = Arrays.asList(strDetails);

} catch (Exception exeption) {
    exeption.printStackTrace();
}

return storeList;

}