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JUnit-如何模拟局部变量对象方法调用

junit5 mockito java

Brother Eye · 技术社区 · 2 年前

我的用例代码如下:

我的班级:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class MyClass {
    public String getString() {
        // object need mocking
        ObjectMapper mapper = new ObjectMapper()
        try {
                          // method need mocking
            return mapper.writeValueAsString(List.of("1", "2"));
        }
        catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }
}

测试代码:

@Test
public void test_get_string() throws Exception {
    ObjectMapper mapper = Mockito.mock(ObjectMapper.class);
    Mockito.when(mapper.writeValueAsString(Mockito.anyList()))
          .thenThrow(JsonProcessingException.class);
    
    Assertions.assertThrows(RuntimeException.class, () -> {
        new MyClass().getString();
    });
    // -> failed
    // Expected RuntimeException but nothing was thrown
}

我想嘲笑 ObjectMapper 并使其投掷 JsonProcessingException 在…上 writeValueAsString 方法调用,但测试一直失败,就好像它根本没有使用我的模拟映射器一样。但是如果我将映射器设为的属性 MyClass 并嘲笑它,然后测试通过。

public class MyClass {
    // make mapper a property
    private ObjectMapper mapper;
    
    public MyClass(ObjectMapper mapper) {
        this.mapper = mapper;
    }

    public String getString() {
        try {
            return mapper.writeValueAsString(List.of("1", "2"));
        }
        catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }
}

@Test
public void test_get_string() throws Exception {
    ObjectMapper mapper = Mockito.mock(ObjectMapper.class);
    Mockito.when(mapper.writeValueAsString(Mockito.anyList()))
          .thenThrow(JsonProcessingException.class);
    
    Assertions.assertThrows(RuntimeException.class, () -> {
        // pass mapper on creating object
        new MyClass(mapper).getString();
    }); // -> success
}

如果我不想让mapper成为我类的一个属性,我应该如何正确地模拟它?

1 回复 | 直到 2 年前

VHS 2 年前

不能使用Mockito模拟方法中声明的局部变量。你可以 ObjectMapper 你班的财产 MyClass 。但如果您不想这样做,另一种选择是在 类名 返回的实例 ObjectMapper

public class MyClass {
    public String getString() {
        // object need mocking
        ObjectMapper mapper = createObjectMapper()
        try {
                          // method need mocking
            return mapper.writeValueAsString(List.of("1", "2"));
        }
        catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }
   protected ObjectMapper createObjectMapper() {
       return new ObjectMapper();
   }
}

然后在您的测试用例中,您可以 spy 您的类并存根这个新方法,以返回一个mocked ObjectMapper 如下所示:

@Test
public void test_get_string() throws Exception {
    ObjectMapper mapper = Mockito.mock(ObjectMapper.class);
    Mockito.when(mapper.writeValueAsString(Mockito.anyList()))
          .thenThrow(JsonProcessingException.class);
    MyClass myClass = Mockito.spy(new MyClass ());
    doReturn(mapper).when(myClass).createObjectMapper();
    Assertions.assertThrows(RuntimeException.class, () -> {
        myClass.getString();
    });
}