如何使用 mockito 模拟字符串?

2022-01-14 00:00:00 mocking unit-testing mockito java

我需要模拟一个测试场景，在该场景中我调用 String 对象的 getBytes() 方法并得到 UnsupportedEncodingException.

I need to simulate a test scenario in which I call the getBytes() method of a String object and I get an UnsupportedEncodingException.

我已尝试使用以下代码来实现:

I have tried to achieve that using the following code:

String nonEncodedString = mock(String.class);
when(nonEncodedString.getBytes(anyString())).thenThrow(new UnsupportedEncodingException("Parsing error."));

问题是，当我运行我的测试用例时，我得到一个 MockitoException，它说我无法模拟 java.lang.String 类.

The problem is that when I run my test case I get a MockitoException that says that I can't mock a java.lang.String class.

有没有办法使用 mockito 来模拟 String 对象，或者，当我调用 getBytes 方法时，是否可以让我的 String 对象抛出 UnsupportedEncodingException?

Is there a way to mock a String object using mockito or, alternatively, a way to make my String object throw an UnsupportedEncodingException when I call the getBytes method?

这里有更多细节来说明问题:

Here are more details to illustrate the problem:

这是我要测试的类:

public final class A {
    public static String f(String str){
        try {
            return new String(str.getBytes("UTF-8"));
        } catch (UnsupportedEncodingException e) {
            // This is the catch block that I want to exercise.
            ...
        }
    }
}

这是我的测试类(我正在使用 JUnit 4 和 mockito):

This is my testing class (I'm using JUnit 4 and mockito):

public class TestA {

    @Test(expected=UnsupportedEncodingException.class)
    public void test(){
        String aString = mock(String.class);
        when(nonEncodedString.getBytes(anyString())).thenThrow(new UnsupportedEncodingException("Parsing error."));
        A.f(aString);
    }
}

推荐答案

问题是Java中的String类被标记为final，所以使用传统的mocking框架不能mock.根据 Mockito FAQ，这也是该框架的限制.

The problem is the String class in Java is marked as final, so you cannot mock is using traditional mocking frameworks. According to the Mockito FAQ, this is a limitation of that framework as well.

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