**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)
this._enqueueCallback(callback, publicInstance);
    this._renderer._newState = completeState;
    this._renderer.render(this._renderer._element, this._renderer._context);
  }
  enqueueSetState(publicInstance, partialState, callback, callerName) {
    this._enqueueCallback(callback, publicInstance);
    const currentState = this._renderer._newState || publicInstance.state;
    if (typeof partialState === 'function') {
      partialState = partialState.call(
        publicInstance,
        currentState,
        publicInstance.props,
      );
    }
    
    if (partialState === null || partialState === undefined) {
      return;
    }
    this._renderer._newState = {
      ...currentState,
      ...partialState,
    };
    this._renderer.render(this._renderer._element, this._renderer._context);
  }
}
function createHook(): Hook {