Wsrtjtyk

I'm not very well-versed with Mockito but am trying to use mocks to test behaviour of a simulation, this is the class:

package simulator;



import java.util.Map;



import org.apache.commons.lang3.Validate;

import simulator.enums.Team;

import simulator.fixtures.Fixture;



public class SimulateBasketballMatchResult implements Simulation<Team> {



    private final Fixture fixture;



    public SimulateBasketballMatchResult(Fixture fixture) {



        Validate.notNull(fixture, "fixture cannot be null");



        this.fixture = fixture;

    }



    @Override

    public Team simulate(Map<Team, Double> outcomeProbabilityMap) {



        Validate.notNull(outcomeProbabilityMap, "outcomeProbabilityMap cannot be null");



        final Team homeTeam = fixture.getHomeTeam();

        final Team awayTeam = fixture.getAwayTeam();



        double random = randomDoubleGenerator();



        double homeWinProbability = outcomeProbabilityMap.get(homeTeam);



        return random < homeWinProbability ? homeTeam : awayTeam;



    }



    public Double randomDoubleGenerator() {

        return Math.random();

    }



}

Below is the test class:

@RunWith(MockitoJUnitRunner.class)

public class SimulateBasketballMatchResultTest {



    @Rule

    public ExpectedException expectedException = ExpectedException.none();



    private static final Map<Team, Double> MATCH_RESULT_PROBABILITY_MAP = new HashMap<>();



    private static final Fixture FIXTURE = new Fixture(GOLDEN_STATE_WARRIORS, HOUSTON_ROCKETS, REGULAR_SEASON);



    static {

        MATCH_RESULT_PROBABILITY_MAP.put(FIXTURE.getHomeTeam(), 0.7d);

        MATCH_RESULT_PROBABILITY_MAP.put(FIXTURE.getAwayTeam(), 0.3d);

    }



    @Mock

    private SimulateBasketballMatchResult simulateBasketballMatchResult;



    @Test

    public void shouldReturnGoldenStateWarriorsAsWinner() {



        when(simulateBasketballMatchResult.randomDoubleGenerator()).thenReturn(0.5d);



        assertThat(simulateBasketballMatchResult.simulate(MATCH_RESULT_PROBABILITY_MAP), is(GOLDEN_STATE_WARRIORS));



    }



}

I would like to assert that GOLDEN_STATE_WARRIORS is returned when the probability range is between 0 and 0.7- however I get an assertion error of null with my test code.

java.lang.AssertionError: 

Expected: is <GOLDEN_STATE_WARRIORS>

     but: was null

Expected :is <GOLDEN_STATE_WARRIORS>

Try this:

@Mock

private Fixture fixture;



private SimulateBasketballMatchResult simulator;



@Before

public void setUp() {

    simulator = spy(new SimulateBasketballMatchResult(fixture));

    doCallRealMethod().when(simulator).simulate();

}



@Test

public void shouldReturnGoldenStateWarriorsAsWinner() {

    doReturn(0.5).when(simulator).randomDoubleGenerator();

    when(fixture.getHomeTeam()).thenReturn(GOLDEN_STATE_WARRIORS);

    when(fixture.getAwayTeam()).thenReturn(HOUSTON_ROCKETS);



    assertThat(simulator.simulate(MATCH_RESULT_PROBABILITY_MAP), is(GOLDEN_STATE_WARRIORS));

}

Mockito.spy and @Spy allow you to mock some methods of a real object, but Mockito.mock and @Mock mock the whole object.

A mock in mockito is a normal mock (allows you to stub invocations; that is, return specific values out of method calls).

A spy in mockito is a partial mock (part of the object will be mocked and part will use real method invocations).

Read more

simulateBasketballMatchResult is a mock object, so by default, it will return null for all its methods (that have a non-primitive return value, of course).

Instead of mocking that object, you should probably spy it:

@Spy

private SimulateBasketballMatchResult simulateBasketballMatchResult = 

    new SimulateBasketballMatchResult(Fixture);