Replace Jasmine+Karma with Mocha+Chai

[nene]

This whole setup for tests feels way too complicated:

• There's little point of using Karma when our tests don't need to run in Browser environment e.g. to interact with DOM.
• Jasmine too is written with browser-testing primarily in mind.
• This whole issue with only one require "babel-polyfill" is a nuisance.

With Mocha one would not need to write any complex configuration files or integrate with Webpack to support ES6. One could use a single command like:

$ mocha --compilers js:babel-register "test/**/*Test.js"

With Chain there's minor difference in the format of assertions, but that mostly means replacing toEqual() with .to.equal().

PS. One thing I don't know about is integration with code coverage - but I suppose it should not be too difficult either.

[bsideup]

I highly recommend you to take a look at Jest, i.e. check how we use it in https://github.com/bsideup/rx-connect .

It has built-in support for babel, coverage, watching, "test only changed", it's browserless, etc...