It is a Jest-ism that shouldn't be in our open source package.
People using Jest can implement a similar pattern directly.
},
  isElement: function(element) {
    return React.isValidElement(element);
  },
  isElementOfType: function(inst, convenienceConstructor) {
    return React.isValidElement(inst) && inst.type === convenienceConstructor;
  },
  isDOMComponent: function(inst) {
    return !!(inst && inst.nodeType === 1 && inst.tagName);
  },
  isDOMComponentElement: function(inst) {
    return !!(inst && React.isValidElement(inst) && !!inst.tagName);
  },
  isCompositeComponent: function(inst) {
    if (ReactTestUtils.isDOMComponent(inst)) {
      
      
      return false;
    }
    return (
      inst != null &&
      typeof inst.render === 'function' &&
      typeof inst.setState === 'function'
    );
  },
  isCompositeComponentWithType: function(inst, type) {
    if (!ReactTestUtils.isCompositeComponent(inst)) {
      return false;
    }
    const internalInstance = ReactInstanceMap.get(inst);