I think this shouldn't pass:

```js
    expect(() => {
      expect(() => {
        throw new Error('haha') // no warning
      }).toWarnDev(
        'nope',
      );
    }).toThrow('haha');
```

but it does.
<ChildUpdates renderAnchor={false} anchorClassOn={true} />,
      container,
    );
    ReactDOM.render(
      
      <ChildUpdates renderAnchor={true} anchorClassOn={false} />,
      container,
    );
    expect(instance.getAnchor().className).toBe('');
  });
  it('should use default values for undefined props', () => {
    class Component extends React.Component {
      static defaultProps = {prop: 'testKey'};
      render() {
        return <span />;
      }
    }
    const instance1 = ReactTestUtils.renderIntoDocument(<Component />);
    expect(instance1.props).toEqual({prop: 'testKey'});
    const instance2 = ReactTestUtils.renderIntoDocument(
      <Component prop={undefined} />,
    );
    expect(instance2.props).toEqual({prop: 'testKey'});
    const instance3 = ReactTestUtils.renderIntoDocument(
      <Component prop={null} />,
    );
    expect(instance3.props).toEqual({prop: null});
  });
  it('should not mutate passed-in props object', () => {
    class Component extends React.Component {