Add test code coverage

[eatrocks]

possibly using nyc

[eatrocks]

The thing about a nyc config using our current webpack setup is that it globs for test files, and follows the imports. This tells us the coverage amount on files that we've chosen to write tests for. So if you have 1 test that 100% tests 1 component, and you have 99 other components that don't have any tests, then your test coverage is 100%.