Using Mockito to stub and execute methods for testing

Question

I ve asked a couple of jUnit and Mockito oriented questions recently and I m still really struggling to get the hang of it  The tutorials are all for very simple examples  so I m struggling to scale up my test cases to work for my classes    I m currently trying to write some test cases for a method I have in one of my agents in a webapp  The method interacts with a couple of other methods inside the agent to validate some objects  I just want to test this one method right now   Here s what I have tried to do    Create a Mockito object of my agent like so   MyProcessingAgent mockMyAgent   Mockito mock MyProcessingAgent class   Setup stubs hopefully the right term  using Mockito when like so   Mockito when mockMyAgent otherMethod Mockito any arg1   thenReturn requiredReturnArg   Try executing my method like so   List myReturnValue   mockMyAgent methodThatNeedsTestCase      I was expecting to things in myReturnValue  but received 0 instead so I tried to debug  When I call the method  it never executes  I have a debug point at the first line in the method that never gets touched   If I want to execute the code in one method of a class  but force other methods in the class  one s that try to interact with databases in the outside world  to return faked out values  Is this possible with Mockito   It appears that my current method of approach is not a correct testing style  but I m not sure how to move forward  Can I mock my class and have one method be executed like normal while other methods are stubbed to return my given values so that I don t have to deal with data access during testing this one method

User · Accepted Answer

You are confusing a Mock with a Spy   In a mock all methods are stubbed and return  smart return types   This means that calling any method on a mocked class will do nothing unless you specify behaviour   In a spy the original functionality of the class is still there but you can validate method invocations in a spy and also override method behaviour   What you want is  MyProcessingAgent mockMyAgent   Mockito spy MyProcessingAgent class     A quick example   static class TestClass        public String getThing             return  Thing              public String getOtherThing             return getThing             public static void main String   args        final TestClass testClass   Mockito spy new TestClass         Mockito when testClass getThing    thenReturn  Some Other thing        System out println testClass getOtherThing         Output is   Some Other thing   NB  You should really try to mock the dependencies for the class being tested not the class itself

User · Answer

So  the idea of mocking the class under test is anathima to testing practice  You should NOT do this  Because you have done so  your test is entering Mockito s mocking classes not your class under test   Spying will also not work because this only provides a wrapper   proxy around the spied class  Once execution is inside the class it will not go through the proxy and therefore not hit the spy  UPDATE  although I believe this to be true of Spring proxies it appears to not be true of Mockito spies  I set up a scenario where method m1   calls m2    I spy the object and stub m2   to doNothing  When I invoke m1   in my test  m2   of the class is not reached  Mockito invokes the stub  So using a spy to accomplish what is being asked is possible  However  I would reiterate that I would consider it bad practice  IMHO    You should mock all the classes on which the class under test depends  This will allow you to control the behavior of the methods invoked by the method under test in that you control the class that those methods invoke   If your class creates instances of other classes  consider using factories

User · Answer

You ve nearly got it  The problem is that the Class Under Test  CUT  is not built for unit testing - it has not really been TDD d   Think of it like this hellip    I need to test a function of a class - let s call it myFunction That function makes a call to a function on another class service database That function also calls another method on the CUT   In the unit test   Should create a concrete CUT or  Spy on it You can  Mock all of the other class service database  i e  external dependencies   You could stub the other function called in the CUT but it is not really how unit testing should be done   In order to avoid executing code that you are not strictly testing  you could abstract that code away into something that can be  Mocked   In this very simple example  a function that creates an object will be difficult to test  public void doSomethingCool String foo        MyObject obj   new MyObject foo           can t do much with obj in a unit test unless it is returned     But a function that uses a service to get MyObject is easy to test  as we have abstracted the difficult impossible to test code into something that makes this method testable   public void doSomethingCool String foo        MyObject obj   MyObjectService getMeAnObject foo       as MyObjectService can be mocked and also verified that  getMeAnObject   is called with the foo variable

User · Answer

SHORT ANSWER  How to do in your case   int argument   5     example with int but could be another type Mockito when mockMyAgent otherMethod Mockito anyInt    thenReturn requiredReturnArg argument      LONG ANSWER  Actually what you want to do is possible  at least in Java 8  Maybe you didn t get this answer by other people because I am using Java 8 that allows that and this question is before release of Java 8  that allows to pass functions  not only values to other functions    Let s simulate a call to a DataBase query  This query returns all the rows of HotelTable that have FreeRoms   X and StarNumber   Y  What I expect during testing  is that this query will give back a List of different hotel  every returned hotel has the same value X and Y  while the other values and I will decide them according to my needs  The following example is simple but of course you can make it more complex   So I create a function that will give back different results but all of them have FreeRoms   X and StarNumber   Y   static List lt Hotel gt  simulateQueryOnHotels int availableRoomNumber  int starNumber        ArrayList lt Hotel gt  HotelArrayList   new ArrayList lt  gt         HotelArrayList add new Hotel availableRoomNumber  starNumber  Rome  1  1        HotelArrayList add new Hotel availableRoomNumber  starNumber  Krakow  7  15        HotelArrayList add new Hotel availableRoomNumber  starNumber  Madrid  1  1        HotelArrayList add new Hotel availableRoomNumber  starNumber  Athens  4  1         return HotelArrayList      Maybe Spy is better  please try   but I did this on a mocked class  Here how I do  notice the anyInt   values      somewhere at the beginning of your file with tests     Mock private DatabaseManager mockedDatabaseManager     in the same file  somewhere in a test    int availableRoomNumber   3  int starNumber   4     in this way  the mocked queryOnHotels will return a different result according to the passed parameters when mockedDatabaseManager queryOnHotels anyInt    anyInt     thenReturn simulateQueryOnHotels availableRoomNumber  starNumber

[java] Using Mockito to stub and execute methods for testing

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