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

User · Answer

With Java 8 it is possible to create a one-line answer even with older version of Mockito:

when(myMock.myFunction(anyString()).then(i -> i.getArgumentAt(0, String.class));

Of course this is not as useful as using AdditionalAnswers suggested by David Wallace, but might be useful if you want to transform argument "on the fly".

User · Answer

I use something similar  basically it s the same approach   Sometimes it s useful to have a mock object return pre-defined output for certain inputs  That goes like this   private Hashtable lt InputObject   OutputObject gt  table   new Hashtable lt InputObject  OutputObject gt     table put input1  ouput1   table put input2  ouput2         when mockObject method any InputObject class    thenAnswer         new Answer lt OutputObject gt                         Override            public OutputObject answer final InvocationOnMock invocation  throws Throwable                             InputObject input    InputObject  invocation getArguments   0                  if  table containsKey input                                       return table get input                                   else                                     return null     alternatively  you could throw an exception

User · Answer

This is a pretty old question but i think still relevant  Also the accepted answer works only for String  Meanwhile there is Mockito 2 1 and some imports have changed  so i would like to share my current answer   import static org mockito AdditionalAnswers returnsFirstArg  import static org mockito ArgumentMatchers any  import static org mockito Mockito when    Mock private MyClass myClass      this will return anything you pass  but it s pretty unrealistic when myClass myFunction any     then returnsFirstArg        it is more  life-like  to accept only the right type when myClass myFunction any ClassOfArgument class    then returnsFirstArg       The myClass myFunction would look like   public class MyClass       public ClassOfArgument myFunction ClassOfArgument argument           return argument

User · Answer

I had a very similar problem  The goal was to mock a service that persists Objects and can return them by their name  The service looks like this   public class RoomService       public Room findByName String roomName            public void persist Room room            The service mock uses a map to store the Room instances   RoomService roomService   mock RoomService class   final Map lt String  Room gt  roomMap   new HashMap lt String  Room gt         mock for method persist doAnswer new Answer lt Void gt           Override     public Void answer InvocationOnMock invocation  throws Throwable           Object   arguments   invocation getArguments            if  arguments    null  amp  amp  arguments length  gt  0  amp  amp  arguments 0     null                Room room    Room  arguments 0               roomMap put room getName    room                     return null           when roomService  persist any Room class        mock for method findByName when roomService findByName anyString     thenAnswer new Answer lt Room gt           Override     public Room answer InvocationOnMock invocation  throws Throwable           Object   arguments   invocation getArguments            if  arguments    null  amp  amp  arguments length  gt  0  amp  amp  arguments 0     null                String key    String  arguments 0               if  roomMap containsKey key                     return roomMap get key                                   return null              We can now run our tests on this mock  For example   String name    room   Room room   new Room name   roomService persist room   assertThat roomService findByName name   equalTo room    assertNull roomService findByName  none

User · Answer

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

User · Answer

You can achieve this by using ArgumentCaptor  Imagine you have bean function like so   public interface Application     public String myFunction String abc       Then in your test class     Use ArgumentCaptor to capture the value ArgumentCaptor lt String gt  param   ArgumentCaptor forClass String class     when mock myFunction param capture     thenAnswer new Answer lt String gt           Override     public String answer InvocationOnMock invocation  throws Throwable         return param getValue     return the captured value                OR if you fan of lambda simply do     Use ArgumentCaptor to capture the value ArgumentCaptor lt String gt  param   ArgumentCaptor forClass String class     when mock myFunction param capture          thenAnswer  invocation  - gt  param getValue       Summary  Use argumentcaptor  to capture the parameter passed  Later in answer return the value captured using getValue

User · Answer

You might want to use verify   in combination with the ArgumentCaptor to assure execution in the test and the ArgumentCaptor to evaluate the arguments   ArgumentCaptor lt String gt  argument   ArgumentCaptor forClass String class   verify mock  myFunction argument capture     assertEquals  the expected value here   argument getValue       The argument s value is obviously accessible via the argument getValue   for further manipulation   checking  whatever

User · Answer

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 lt String gt           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 - gt  i getArguments   0

User · Answer

With Java 8  Steve s answer can become    public void testMyFunction   throws Exception       Application mock   mock Application class       when mock myFunction anyString     thenAnswer      invocation - gt            Object   args   invocation getArguments            return args 0                assertEquals  someString   mock myFunction  someString         assertEquals  anotherString   mock myFunction  anotherString         EDIT  Even shorter     public void testMyFunction   throws Exception       Application mock   mock Application class       when mock myFunction anyString     thenAnswer          invocation - gt  invocation getArgument 0         assertEquals  someString   mock myFunction  someString         assertEquals  anotherString   mock myFunction  anotherString

User · Answer

This is a bit old  but I came here because I had the same issue  I m using JUnit but this time in a Kotlin app with mockk  I m posting a sample here for reference and comparison with the Java counterpart    Test fun demo          mock a sample function   val aMock   String  - gt   String    mockk         make it return the same as the argument on every invocation   every       aMock invoke any        answers       firstArg             test it   assertEquals  senko   aMock invoke  senko      assertEquals  senko1   aMock invoke  senko1      assertNotEquals  not a senko   aMock invoke  senko

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

Examples related to java

Examples related to mockito