Creating stub for dependence class's under test

Question

Good day, everyone! I have a little question about testing and generating a stub for dependence through reflection. So let's assume I have a class named UnderTest:

class UnderTest{
/*field*/ 
SomeLogic someLogic; 
/*method, that i testing*/
List<MyObject> getCalculatedObjects(params) {/*logic,based on result getSomeStuff of someLogic*/    }
} 
class SomeLogic { 
List<String> getSomeStuff(String param) { /*Some complex and slow code, actually  don't want test this code, and want to use some reflection invocation handler*/ }
}

For me it's important to not change legacy code, which doesn't design for testing. And i don't have any reason, except testing to make SomeLogic as an interface and so on. I can't remember how to handle method invocation of someLogic using reflection. But google search isn't helping me.

Class MainAPI is... main api of my module. NetworkProvider long open stream operation, that's why i want to stub it, on my local files. But don't using directly reference on NetworkProvider. Again sorry for my English.

public class MainAPI {
    private final XPath xPath;
    private final ItemParser itemParser;
    private final ListItemsParser listItemsParser;
    private final DateParser dateParser;
    private final HtmlCleanUp htmlCleanUp;

    private final NetworkProvider networkProvider;


    public MainAPI(XPath xPath, ItemParser itemParser, ListItemsParser listItemsParser, DateParser dateParser, HtmlCleanUp htmlCleanUp, NetworkProvider networkProvider) {
        this.xPath = xPath;
        this.itemParser = itemParser;
        this.listItemsParser = listItemsParser;
        this.dateParser = dateParser;
        this.htmlCleanUp = htmlCleanUp;
        this.networkProvider = networkProvider;
    }

    public MainAPI() throws XPathExpressionException, IOException {
        dateParser = new DateParser();
        xPath = XPathFactory.newInstance().newXPath();
        networkProvider = new NetworkProvider();
        listItemsParser = new ListItemsParser(xPath, dateParser, item -> true);
        itemParser = new ItemParser(xPath, dateParser, networkProvider);
        htmlCleanUp = new HtmlCleanUpByCleaner();
    }

    public List<Item> getItemsFromSessionParsing(SessionParsing sessionParsing) {
        listItemsParser.setCondition(sessionParsing.getFilter());
        List<Item> result = new ArrayList<>();
        Document cleanDocument;
        InputStream inputStream;
        for (int currentPage = sessionParsing.getStartPage(); currentPage <= sessionParsing.getLastPage(); currentPage++) {
            try {
                inputStream = networkProvider.openStream(sessionParsing.getUrlAddressByPageNumber(currentPage));
            } catch (MalformedURLException e) {
                e.printStackTrace();
                break;
            }
            cleanDocument = htmlCleanUp.getCleanDocument(inputStream);
            List<Item> list = null;
            try {
                list = listItemsParser.getList(cleanDocument);
            } catch (XPathExpressionException e) {
                e.printStackTrace();
                break;
            }
            for (Item item : list) {
                inputStream = null;
                try {
                    inputStream = networkProvider.openStream("http://www.avito.ru" + item.getUrl());
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                    break;
                }
                cleanDocument = htmlCleanUp.getCleanDocument(inputStream);
                try {
                    item.setDescription(itemParser.getDescription(cleanDocument));
                } catch (XPathExpressionException e) {
                    e.printStackTrace();
                }

            }
            result.addAll(list);
        }
        return result;
    }
}

public class NetworkProvider {
    private final ListCycleWrapper<Proxy> proxyList;

    public NetworkProvider(List<Proxy> proxyList) {
        this.proxyList = new ListCycleWrapper<>(proxyList);
    }

    public NetworkProvider() throws XPathExpressionException, IOException {
        this(new ProxySiteParser().getProxyList(new HtmlCleanUpByCleaner().getCleanDocument(new URL("http://www.google-proxy.net").openStream())));
    }

    public int getSizeOfProxy() {
        return proxyList.size();
    }

    public InputStream openStream(String urlAddress) throws MalformedURLException {
        URL url = new URL(urlAddress);

        while (!proxyList.isEmpty()) {
            URLConnection con = null;
            try {
                con = url.openConnection(proxyList.getNext());
                con.setConnectTimeout(6000);
                con.setReadTimeout(6000);
                return con.getInputStream();
            } catch (IOException e) {
                proxyList.remove();
            }
        }
        return null;
    }
}

Answer 1

All the dependencies of your class to tests are injectable using its constructor, so there shouldn't be any problem to stub these dependencies and injecting the stubs. You don't even need reflection. For example, using Mockito:

NetworkProvider stubbedNetworkProvider = mock(NetworkProvider.class);
MainAPI mainApi = new MainAPI(..., stubbedNetworkProvider);

You can also write a stub by yourself if you want:

NetworkProvider stubbedNetworkProvider = new NetworkProvider(Collections.emptyList()) {
    // TODO override the methods to stub
};
MainAPI mainApi = new MainAPI(..., stubbedNetworkProvider);