JMockit to Mockito - rewrite expectation results with the correct type

What problem are you trying to solve?

Within an Expectations block in JMockit, we can record method invocations and the expected result. JMockit has some internal logic to handle cases where there is a type mismatch between the result and the return type of the method and performs auto conversion.

Raising this ticket to kick off a discussion about creating a standalone recipe to clean this up or to add to the existing recipe created here - https://github.com/openrewrite/rewrite-testing-frameworks/pull/415

See https://javadoc.io/static/org.jmockit/jmockit/1.49/mockit/Expectations.html#result for more info

Example

Consider the following class below:

class SomeObject {
        public long longMethod() {
            return 1L;
        }

        public List<Long> listMethod() {
            return Arrays.asList(1L);
        }
}

A test mocking the methods above might look something like follows:

@Injectable SomeObject someObject;

@Test
void test() {

    new Expectations() {{
        someObject.longMethod();
        result = 1;

        someObject.listMethod();
        result = 2;
    }};

    ....
}

Running the existing JMockitExpectationsToMockito recipe

@Mock SomeObject someObject;

@Test
void test() {
    
    when(someObject.longMethod()).thenReturn(1);  // Should be converted to the long literal 1L 
    when(someObject.listMethod()).thenReturn(2);  // Also doesn't compile because of type mismatch
    
   ...
}

As you can see above, the existing recipe to rewrite expectations doesn't account for this type conversion. Should we look at creating a separate recipe to first look at fixing up these issues and then apply the JMockitExpectationsToMockito recipe?

Are you interested in contributing this recipe to OpenRewrite?

Yes

Start by reading the existing JMockitExpectationsToMockito recipe and the related pull request 415, then compare its handling of result assignments with the examples in this issue. Clarify whether the type corrections belong in that recipe or a separate one; done means the converted long and List expectations compile with the correct Mockito return expressions.