It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
super();
            this.state = {value: 'Hello'};
          }
          handleChange(event) {
            if (this.props.onChange) {
              this.props.onChange(event);
            }
            this.setState({value: event.target.value});
          }
          render() {
            return (
              <select
                value={this.state.value}
                onChange={this.handleChange.bind(this)}>
                <option key="1" value="Hello">Hello</option>
                <option key="2" value="Goodbye">Goodbye</option>
              </select>
            );
          }
        };
      });
      describe('user interaction with controlled inputs', function() {
        itClientRenders('a controlled text input', async render => {
          let changeCount = 0;
          const e = await render(
            <ControlledInput onChange={() => changeCount++} />,
          );
          expect(changeCount).toBe(0);