code: function validateChoices(props, propName, componentName) {
    const propValue = props[propName];
    if (!propValue) {
      return undefined;
    }
  
    if (!Array.isArray(propValue) || propValue.length !== 2) {
      return new Error(`Invalid ${propName} supplied to \`${componentName}\`, expected exactly two Choice components.`);
    }
  
    for (let i = 0; i < propValue.length; ++i) {
      const item = propValue[i];
      if (!item || !isComponentOfType(Choice, item)) {
        return new Error(`Invalid ${propName}[${i}] supplied to \`${componentName}\`, expected a Choice component from Belle.`);
      }
    }
  
    if (first(propValue).props.value === last(propValue).props.value) {
      return new Error(`Invalid ${propName} supplied to \`${componentName}\`, expected different value properties for the provided Choice components.`);
    }
  
    return undefined;
  }
docs: Verifies that the children is an array containing only two choices with a
  different value.