Pretty-print React instances.

[cpojer]

See jestjs/jest#1429

[jamiebuilds]

Should maybe test with an array as the child as well

React.createElement('div', null, 'mouse', [
  React.createElement('span', null, 'rat'),
  React.createElement('span', null, 'squirrel')
])

[cpojer]

Ok this works but only for host objects and not for components. When using React.createElement(Button) as a prop, it will print the class source which is definitely not what we want.

@gaearon I think I need more input on this. Should we only print the top level component? @thejameskyle said that a general React printing plugin should be more complex than that but I'd really like to avoid digging into the internal React structure because that will just get us into trouble. Should the test-renderer do something with those and just throw away the instance data?

[gaearon]

Let's chat in person. I think you may be confusing elements and instances :-)