State is always initialized under shallow

[abettadapur]

Describe the bug
I have a component that does not initialize any state.

If I shallow mount this component, when render is called, this.state has a {} value, even though I did not initialize it.

Repro:

const Enzyme = require("enzyme");
const React = require("react");
class Foo extends React.Component {
    constructor(props, context) {
        super(props, context);
    }
    render() {
        console.log(`State: ${JSON.stringify(this.state)}`); // prints State: {}
        return (React.createElement("div", null));
    }
}
it("Test render", () => {
    Enzyme.shallow(React.createElement(Foo, null));
});

Expected behavior
this.state should be undefined

** Versions **
Enzyme: 3.3.2
Enzyme-Adapter-React-16: 1.5.0

[ljharb]

See https://jsfiddle.net/69z2wepo/310645/ - it looks like this.state starts out null when you don't specify it.

I've added some tests that verify this, which seem to be passing locally.

Can you try updating to the latest enzyme (v3.6.0)?

[abettadapur]

I will upgrade and see.
The state may not be undefined, but it should not be {}

[ljharb]

Very true; it looks like actually in React 16.0 - 16.3 this might be the case (please fill out the entire issue template). What React version are you using?

[ljharb]

Turns out this is a bug in the React shallow renderer, fixed in facebook/react#11965.

I'll see if I can fix it in the 16.0, 16.1, and 16.2 adapters.

[abettadapur]

@ljharb Thanks for the quick turnaround

Just to close the loop, when will the fix appear in the adapter packages?

[ljharb]

The next release will include it; hopefully it will be in the next couple days.

[abettadapur]

@ljharb Thanks! Appreciate the quick response