How to mock a String using mockito?

Question

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

I have tried to achieve that using the following code:

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

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.

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?

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Here are more details to illustrate the problem:

This is the class that I want to test:

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.             ...         }     } } 

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);     } } 

Answer 1

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.