import org.junit.Test;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import static org.mockito.Mockito.when;

public class MockitoDemo {

    static class ExampleService {

        public void hello() {
            System.out.println("Hello");
        }

    }

    @Mock
    private ExampleService exampleService;

    @Test
    public void test() {

        MockitoAnnotations.initMocks(this);

        // 这句编译不通过，IDE 也会提示错误，原因很简单，when 的参数是非 void
        when(exampleService.hello()).thenThrow(new RuntimeException("异常"));

    }

}

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

import static org.mockito.Mockito.doThrow;

public class MockitoDemo {

    static class ExampleService {

        public void hello() {
            System.out.println("Hello");
        }

    }

    @Mock
    private ExampleService exampleService;

    @Test
    public void test() {

        MockitoAnnotations.initMocks(this);

        // 这种写法可以达到效果
        doThrow(new RuntimeException("异常")).when(exampleService).hello();

        try {
            exampleService.hello();
            Assert.fail();
        } catch (RuntimeException ex) {
            Assert.assertEquals("异常", ex.getMessage());
        }

    }

}

import org.junit.Assert;
import org.junit.Test;
import org.mockito.MockitoAnnotations;

import java.util.Random;

import static org.mockito.Mockito.*;

public class MockitoDemo {

    @Test
    public void test() {

        MockitoAnnotations.initMocks(this);

        Random random = mock(Random.class);

        // 下面这句等同于 when(random.nextInt()).thenThrow(new RuntimeException("异常"));
        doThrow(new RuntimeException("异常")).when(random).nextInt();

        try {
            random.nextInt();
            Assert.fail();
        } catch (RuntimeException ex) {
            Assert.assertEquals("异常", ex.getMessage());
        }

    }

}