Commit 6a489d9 broke unit tests

[AlwaysMoreHats]

Unit tests have been broken since this commit.

Broken with error TypeError: Cannot read property '1' of undefined in getElementHeight, line 61

[AlwaysMoreHats]

Adding in jest.dontMock('element-size'); on the unit tests fixes this error, but uncovers a new error:

TypeError: Cannot call method 'getDOMNode' of undefined in getChildHeight line 132

The same commit is the culprit, see here: https://github.com/BI/react-lazy-render/tree/unit-test-fix

[AlwaysMoreHats]

Last one (I hope): TypeError: Cannot call method 'getDOMNode' of undefined

This is being caused because:

1. componentDidMount calls getChildHeight to initially set the child height
2. getChildHeight calls getElementHeight to get the measured height
3. getElementHeight calls into element-size module to get the measured height
4. element-size module calls element.getBoundingClientRect
5. Elements in the testing environment return 0 for all values in the bounding rect
6. height: 0 gets passed back up, which causes the next pass (i.e. the update, which happens immediately after the mount), to attempt to render 0 elements
7. because there are no elements, no children render, thus no refs can be found