New toBeEmpty custom matcher

[gnapse]

As discussed in #4, this library needs some sort of .toBeEmpty custom matcher. This will pass if the given element does not contain any child elements.

expect(element).toBeEmpty()

A few aspects of this are open to discussion. We'd like to come up with a different name that would be clearer and avoid name clashes with other matchers out there that might be checking emptiness of other things (e.g. array or collections of some sort).

How?

// TODO

Why?

Presumably doing the equivalent checks on one's own is not straightforward and concise enough.

[smacpherson64]

@gnapse with empty does this mean text nodes as well as element nodes?

If we want no text and elements we could use: element.innerHTML === ''
If we want no element children we could use element.children.length === 0

[kentcdodds]

As a user I would expect empty to mean that element.innerHTML === ''

[smacpherson64]

Sounds good!