Tests

NOTE: This should be merged after !71 (merged).

Rolled up my sleeves and did the fastidious but interesting job of writing down missing tests.

The code coverage significantly improves from ~20% to ~80%. You should keep in mind that the missing 20% are mostly due to using shallow() instead of mount() for most of our components, which is a good thing but does not mount/test the inner styling components. So most of the missing coverage is on Component.style.js files, which is very fine.

Fixes #43 (closed)