[FIXED] Mockito mocking a new instance call with parameters

Issue

For school purposes I am creating an application that's working with a stock API.

I am trying to write a test for a method that gets all the stock data of the last 10 years. Instead of actually getting all that data, I want to throw an exception.

The method I Want to test:

@Override
public List<StockData> getAllTeslaStockData() throws AlphaVantageException {
    List<StockData> stockData;

    AlphaVantageConnector apiConnector = new AlphaVantageConnector(APIKEY, TIMEOUT);
    TimeSeries stockTimeSeries = new TimeSeries(apiConnector);

    try {

        Daily responseDaily = stockTimeSeries.daily("TSLA", OutputSize.FULL);
        stockData = responseDaily.getStockData();

    } catch (AlphaVantageException e) {

        LOGGER.log(Level.SEVERE, "something went wrong: ", e);

        throw e;

    }

    return stockData;
}

The stockTimeSeries.daily(....) call can throw the AlphaVantageException.

I've mocked the TimeSeries class like this:

TimeSeries stockTimeSeries = mock(TimeSeries.class);

In my test class I want to mock this call, and return an exception instead of actual data.

when(stockTimeSeries.daily("TSLA", OutputSize.FULL)).thenThrow(new AlphaVantageException("No stock data available"));

Regardless of how I am trying to mock this bit of code, it'll never throw the exception. It will always just execute the code, and return valid stock data, instead of throwing the exception like i've tried to do.

How can I mock this bit of code, so that itll throw the exception I am expecting for my tests.

The AlphaVantageConnector, TimeSeries and Daily classes are part of a library used to access the stock API, so I can't change these classes.

I am using JUnit 4.12 and Mockito to try and achieve this.

Solution

The TimeSeries object is created in the method itself, so you can't mock it - mocking is intended to mock members.

What you can do is to do something like

class YourClass {
   private Supplier<TimeSeries> seriesCreator = () -> {
       return new TimeSeries(new AlphaVantageConnector(APIKEY, TIMEOUT));
   }

which you use to create the series in your method

@Override
public List<StockData> getAllTeslaStockData() throws AlphaVantageException {
    TimeSeries stockTimeSeries = seriesCreator.get();

Now you can mock that Supplier.

@Mock Supplier<TimeSeries> seriesCreatorMock;
@InjectMocks MyClass sut;

and in your test

@Test(expected = AlphaVantageException.class)
void testException() {
    when(seriesCreatorMock.get()).thenThrow(new AlphaVantageException());
    sut.getAllTeslaStockData()
}

EDIT: as suggested by Angkur in the comments, the clean way would be to

class SeriesCreator implements Supplier<TimeSeries> {
    public TimeSeries get() {
       return new TimeSeries(new AlphaVantageConnector(APIKEY, TIMEOUT));
    }
}

class YourClass {
   private Supplier<TimeSeries> seriesCreator = new SeriesCreator();

// ...

Answered By - daniu
Answer Checked By - Mildred Charles (JavaFixing Admin)