Making a mocked method return an argument that was passed to it

Question

Consider a method signature like:

public String myFunction(String abc); 

Can Mockito help return the same string that the method received?

Answer 1

You can create an Answer in Mockito. Let's assume, we have an interface named Application with a method myFunction.

public interface Application {   public String myFunction(String abc); } 

Here is the test method with a Mockito answer:

public void testMyFunction() throws Exception {   Application mock = mock(Application.class);   when(mock.myFunction(anyString())).thenAnswer(new Answer<String>() {     @Override     public String answer(InvocationOnMock invocation) throws Throwable {       Object[] args = invocation.getArguments();       return (String) args[0];     }   });    assertEquals("someString",mock.myFunction("someString"));   assertEquals("anotherString",mock.myFunction("anotherString")); } 

Since Mockito 1.9.5 and Java 8, you can also use a lambda expression:

when(myMock.myFunction(anyString())).thenAnswer(i -> i.getArguments()[0]); 

Answer 2

If you have Mockito 1.9.5 or higher, there is a new static method that can make the Answer object for you. You need to write something like

import static org.mockito.Mockito.when; import static org.mockito.AdditionalAnswers.returnsFirstArg;  when(myMock.myFunction(anyString())).then(returnsFirstArg()); 

or alternatively

doAnswer(returnsFirstArg()).when(myMock).myFunction(anyString()); 

Note that the returnsFirstArg() method is static in the AdditionalAnswers class, which is new to Mockito 1.9.5; so you'll need the right static import.