**Do you want to request a *feature* or report a *bug*?**
bug

**What is the current behavior?**
In normal rendering, you can memoize a class-based component: https://jsfiddle.net/586ea3cx/

With the shallow renderer, it seems like you can't: https://jsfiddle.net/odj217Lv/1/

This might be blocking https://github.com/airbnb/enzyme/pull/1914, in which tests are failing with `Cannot call a class as a function`. (it's tough to repro stuff with the shallow renderer)
return prevState[0];
          }
        }
      }
      const nextValue = nextCreate();
      (this._workInProgressHook: any).memoizedState = [nextValue, nextDeps];
      return nextValue;
    };
    const useRef = <T>(initialValue: T): {current: T} => {
      this._validateCurrentlyRenderingComponent();
      this._createWorkInProgressHook();
      const previousRef = (this._workInProgressHook: any).memoizedState;
      if (previousRef === null) {
        const ref = {current: initialValue};
        if (__DEV__) {
          Object.seal(ref);
        }
        (this._workInProgressHook: any).memoizedState = ref;
        return ref;
      } else {
        return previousRef;
      }
    };
    const readContext = <T>(