Enzyme: Calling `setProps` on shallow wrapper results in `componentDidUpdate` being called twice

[jpmoral]

Describe the bug
Calling setProps on a shallow wrapper results in componentDidUpdate being called twice (instead of once).

To Reproduce
Steps to reproduce the behavior:
Run the test:

import React from 'react';


export default class Dummy extends React.Component {
    componentWillReceiveProps(nextProps) {
        this.setState({someState: nextProps.myProp});
    }

    componentDidUpdate() {
        this.foo();
    }

    foo() {}

    render() {
        return (
            <div>
                <div>{`myProp: ${this.props.myProp}`}</div>
            </div>
        );
    }
}

import React from 'react';
import {shallow} from 'enzyme';

import Dummy from 'dummy.js';


describe('<Dummy/>', () => {
    it('works', () => {
        const props = {};
        const wrapper = shallow(<Dummy {...props} />);
        wrapper.instance().foo = jest.fn();
        wrapper.setProps({myProp: 'Prop Value'});
        expect(wrapper.instance().foo).toHaveBeenCalledTimes(1);
    });
});

Expected behavior
componentDidUpdate should only be called once.

Desktop (please complete the following information):

• OS: macOS Mojave
• Browser n/a
• Version 3.7.0

Smartphone (please complete the following information):
n/a

[ljharb]

(wrapper.instance().foo = jest.fn(); isn't doing what you think it is; you need to spy on Dummy.prototype.foo before the initial render)

It seems like the issue is that it's calling cWRP, queueing up a setState, rerendering with the props only, and calling cDU, and then rerendering with the new state, and then calling cDU again.

I presume that React itself is batching up the updates so that this is working as expected - I don't believe we have proper batching support for React 16 just yet.

(cc @koba04)

[ljharb]

What happens when you use mount?

[koba04]

@ljharb
Yeah, React doesn't support batched updates on ShallowRendering from v16.

https://github.com/facebook/react/issues/10355

So currently, it's a no-op.

https://github.com/airbnb/enzyme/blob/master/packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js#L327-L330

If we support batching updates on shallow to fix this, we have to implement ourselves.

[ljharb]

Although that's a lot more work, I think it's probably worth it so that things are consistent between React and enzyme.

[jpmoral]

@ljharb thanks, mount works. I've edited the title and body to explicitly mention shallow.

[peanutenthusiast]

I'll go ahead and look into this issue if a fix hasn't already been applied.

[peanutenthusiast]

@ljharb Added the above test case, but in terms of the fix, has there been much discussion on adding support for batched updates with the ReactSixteenThreeAdapter?

I've been looking at @koba04's implementation of unstable_batchedUpdates

https://github.com/koba04/react/commit/ca78c92635525ad2dfd8012e7e5527a5876ce130,

but would you have any suggestions for moving forward?

[ljharb]

@peanutenthusiast not much, but I'd love to add it (ideally separate from bug fixes)

[peanutenthusiast]

Was out of country for a month or so, but I've come up with a fix for the above test case -- @ljharb are there any other test cases that should be covered? I can send a PR tonight.

[ljharb]

Not that i know of; PR away!

[jpmoral]

Awesome, thanks everyone!