initMocks

MockTest.java

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.mockito.Mock;

import java.util.List;

import static org.mockito.ArgumentMatchers.anyInt;
import static org.mockito.Mockito.when;
import static org.mockito.MockitoAnnotations.initMocks;


public class MockTest {
    @Mock
    private List mockedList;

    @Before
    public void setUp() {
        // これがないとmockedListはnullのまま
        initMocks(this);
    }

    @Test
    public void test1() {
        when(mockedList.get(anyInt()))
                .thenReturn(500);

        Object actual = mockedList.get(120);

        Assert.assertEquals(500, actual);
    }

}