class ComponentToBeTested extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      isActive: false
    };
    this.handleButtonClick = this.handleButtonClick.bind(this);
  }

  handleButtonClick() {
    this.setState({
      isActive: !this.state.isActive
    });
  }

  multiply(data) {
    return data * 10;
  }

  square(data) {
    return Math.pow(data, 2);
  }

  render() {
    const givenData = this.props.data;
    const multipliedData = this.multiply(givenData);
    const squaredData = this.square(givenData);

    return (
      <div className="ComponentToBeTested">
        <button className="test-button" onClick={this.handleButtonClick}>
          FOO
        </button>
        <ChildComponent data={multipliedData} />
        <span className="squared-data">{squaredData}</span>
      </div>
    );
  }