Mockito - intercept any method invocation on a mock

Question

Is it possible to intercept all method invocations on a mock in a generic way?

Example

Given a vendor provided class such as:

public class VendorObject {      public int someIntMethod() {         // ...     }      public String someStringMethod() {         // ...     }  } 

I would like to create a mock that re-directs all method calls to another class where there are matching method signatures:

public class RedirectedToObject {      public int someIntMethod() {         // Accepts re-direct     }  } 

The when().thenAnswer() construct in Mockito seems to fit the bill but I cannot find a way to match any method call with any args. The InvocationOnMock certainly gives me all these details anyway. Is there a generic way to do this? Something that would look like this, where the when(vo.*) is replaced with appropriate code:

VendorObject vo = mock(VendorObject.class); when(vo.anyMethod(anyArgs)).thenAnswer(     new Answer() {         @Override         public Object answer(InvocationOnMock invocation) {              // 1. Check if method exists on RedirectToObject.             // 2a. If it does, call the method with the args and return the result.             // 2b. If it does not, throw an exception to fail the unit test.          }     } ); 

Adding wrappers around the vendor classes to make mocking easy is not an option because:

1. Too large an existing code base.
2. Part of extremely performance critical applications.

Answer 1

I think what you want is:

VendorObject vo = mock(VendorObject.class, new Answer() {     @Override     public Object answer(InvocationOnMock invocation) {          // 1. Check if method exists on RedirectToObject.         // 2a. If it does, call the method with the args and return the         // result.         // 2b. If it does not, throw an exception to fail the unit test.      } }); 

Of course, if you want to use this approach frequently, no need for the Answer to be anonymous.

From the documentation: "It's quite advanced feature and typically you don't need it to write decent tests. However it can be helpful when working with legacy systems." Sounds like you.