Add tap() into ShallowWrapper and ReactWrapper

[koba04]

This is similar to underscore's tap().

http://underscorejs.org/#tap

motivation

When I'm testing complex React Element tree using method chains, I sometimes would like to inject a debug code between the method chains.

wrapper
.find('.foo')
.findWhere(n => n.text() === 'bar')
// ???
.at(0)

• Using tap()

wrapper
.find('.foo')
.findWhere(n => n.text() === 'bar')
.tap(n => console.log(n.debug())
.at(0)

• without tap()

wrapper
.find('.foo')
.findWhere(n => n.text() === 'bar')
.map(n => {
  console.log(n.debug());
  return n;
})
.at(0)

I think this is not an essential feature, but it would be nice if enzyme has it.
How do you think about this? 👍? 👎?

Thanks.

[ljharb]

expect(spy.calledWith(wrapper)).to.equal(true) might be a stronger assertion?

[koba04]

Thanks! I fixed it.

[ljharb]

I think this is a pretty useful feature to be sure.

[lelandrichardson]

I like this as well. Never knew about this w/ underscore.

@koba04 do you mind rebasing before we merge in? Thanks.

[koba04]

@lelandrichardson Thank you! rebased.