Can you create this model in the same style above?

Also, is it possible to extract `target` and `source` into a before block like so

```objc
__block MTLTestModel *super;
__block MTLSubclassTestModel *subclass;

beforeEach(^{
    super = [MTLTestModel modelWithDictionary:@{
        @"name": @"foo",
        @"count": @5
    } error:NULL];

    expect(super).notTo.beNil();

    subclass = [MTLSubclassTestModel modelWithDictionary:@{
        @"name": @"bar",
        @"count": @3,
        @"generation": @1,
        @"role": @"subclass"
    } error:NULL];

    expect(subclass).notTo.beNil();
})
```