Tests for the love of dog, tests

[bradparker]

Testing webpack output is possible. Just needs to be setup.

With webpack you can specify both an input and output filesystem. Allowing us to mock the filesystem into memory entirely using say: https://github.com/webpack/memory-fs

The below shows that inputFileSystem and outputFileSystem are public attributes of compiler instances.
https://github.com/webpack/webpack/blob/90d537ef4ce1092f76bd02ee2a75838c67b809fc/lib/Compiler.js#L148-L149

[bradparker]

I'll use this to keep track of tests which I think are missing.
We still need some tests to ensure that a basic set of plugins / loaders are being included from createConfigs