Calling setState in componentWillMount crashes skin-deep

[nikcorg]

We recently upgraded out React dependency to 0.14. To my surprise this caused some of our skin-deep powered tests to fail with TypeError: Cannot read property '_currentElement' of null.

The skin-deep test suite passes with flying colours in our setup, so I was a bit stumped. Eventually I found the cause of the error to be a call to setState in componentWillMount.

The error originates in react/lib/ReactCompositeComponent, which is why I'm unsure of whether I should be reporting it here or rather to the React project. If I'm in the wrong place, speak up and I will move on.

See a failing test below this line.

import React, { Component } from "react"; // 0.14
import test from "tape";
import sd from "skin-deep";

class FailingComp extends Component {
    constructor(props) {
        super(props);
        this.state = {};
    }
    componentWillMount() {
        // comment the line below to pass the test
        this.setState({ hello: "World!" });
    }
    render() {
        const { hello = "World" } = this.state;
        return <p>{`Hello ${hello}!`}</p>;
    }
}

test("component", t => {
    const render = (props = {}) => {
        const tree = sd.shallowRender(React.createElement(FailingComp, props));
        const inst = tree.getMountedInstance();
        const vdom = tree.getRenderOutput();

        return { tree, inst, vdom };
    };

    const { vdom } = render();

    t.equal(vdom.type, "p", "renders p-tag");
    t.deepEqual(vdom.props.children, "Hello World!", "contains the text 'Hello World!'");
    t.end();
});

[glenjamin]

This is a bug in React itself, see facebook/react#4019 (comment) for a workaround

[nikcorg]

Though it might be. Thanks.