Create new test suite with babel-plugin-tester

[tleunen]

In the long term, I believe it will be easier to maintain tests with babel-plugin-tester, so I've taken the work that has been started in #284 and updated the test suite.

It seems there's now a breaking test when @babel/plugin-transform-modules-commonjs is also used. I'll need to take a deeper look at it.

If you have any idea @fatfisz, your help will be very appreciated :)