Mocking methods of local scope objects with Mockito

Question

I need some help with this   Example   void method1      MyObject obj1 new MyObject        obj1 method1        I want to mock obj1 method1   in my test but to be transparent so I don t want make and change of code  Is there any way to do this in Mockito

User · Answer

No way  You ll need some dependency injection  i e  instead of having the obj1 instantiated it should be provided by some factory  MyObjectFactory factory   public void setMyObjectFactory MyObjectFactory factory      this factory   factory     void method1       MyObject obj1   factory get      obj1 method       Then your test would look like   Test public void testMethod1   throws Exception     MyObjectFactory factory   Mockito mock MyObjectFactory class     MyObject obj1   Mockito mock MyObject class     Mockito when factory get    thenReturn obj1           mock the method     Mockito when obj1 method    thenReturn Boolean FALSE      SomeObject someObject   new SomeObject      someObject setMyObjectFactory factory     someObject method1          do some assertions

User · Answer

You can do this by creating a factory method in MyObject   class MyObject       public static MyObject create           return new MyObject              then  mock that with PowerMock   However  by mocking the methods of a local scope object  you are depending on that part of the implementation of the method staying the same   So you lose the ability to refactor that part of the method without breaking the test   In addition  if you are stubbing return values in the mock  then your unit test may pass  but the method may behave unexpectedly when using the real object   In sum  you should probably not try to do this   Rather  letting the test drive your code  aka TDD   you would arrive at a solution like   void method1 MyObject obj1       obj1 method1        passing in the dependency  which you can easily mock for the unit test

User · Answer

The answer from  edutesoy points to the documentation of PowerMockito and mentions constructor mocking as a hint but doesn t mention how to apply that to the current problem in the question  Here is a solution based on that  Taking the code from the question  public class MyClass       void method1           MyObject obj1   new MyObject            obj1 method1             The following test will create a mock of the MyObject instance class via preparing the class that instantiates it  in this example I am calling it MyClass  with PowerMock and letting PowerMockito to stub the constructor of MyObject class  then letting you stub the MyObject instance method1   call   RunWith PowerMockRunner class   PrepareForTest MyClass class  public class MyClassTest        Test     public void testMethod1                   MyObject myObjectMock   mock MyObject class           when myObjectMock method1    thenReturn  lt whatever you want to return gt               PowerMockito whenNew MyObject class  withNoArguments   thenReturn myObjectMock                    MyClass objectTested   new MyClass            objectTested method1                            your assertions or verification here           With that your internal method1   call will return what you want  If you like the one-liners you can make the code shorter by creating the mock and the stub inline  MyObject myObjectMock   when mock MyObject class  method1    thenReturn  lt whatever you want gt   getMock

User · Answer

You could avoid changing the code  although I recommend Boris  answer  and mock the constructor  like in this example for mocking the creation of a File object inside a method  Don t forget to put the class that will create the file in the  PrepareForTest  package hello easymock constructor   import java io File   import org easymock EasyMock  import org junit Assert  import org junit Test  import org junit runner RunWith  import org powermock api easymock PowerMock  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner        RunWith PowerMockRunner class   PrepareForTest  File class   public class ConstructorExampleTest                 Test     public void testMockFile   throws Exception               first  create a mock for File         final File fileMock   EasyMock createMock File class           EasyMock expect fileMock getAbsolutePath    andReturn  quot  my fake file path quot            EasyMock replay fileMock               then return the mocked object if the constructor is invoked         Class lt   gt    parameterTypes   new Class     String class            PowerMock expectNew File class  parameterTypes   EasyMock isA String class   andReturn fileMock           PowerMock replay File class                    try constructing a real File and check if the mock kicked in         final String mockedFilePath   new File  quot  real path for file quot   getAbsolutePath            Assert assertEquals  quot  my fake file path quot   mockedFilePath

User · Answer

If you really want to avoid touching this code  you can use Powermockito  PowerMock for Mockito    With this  amongst many other things  you can mock the construction of new objects in a very easy way

[object] Mocking methods of local scope objects with Mockito

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