Rewrite all tests as blackbox

There are two types of tests in Radium.

1. The older, whitebox, tests that require internal modules and test them individually. These tests are fragile and hard to maintain, relying on module injection. Even worse, they don't represent real usage.
2. The newer, blackbox, tests, which test Radium exactly as external callers would (using the decorator or wrapper function). The new tests are easier to write, since they are using the public API, and represent actual use cases for Radium.

We should rewrite the entire test suite, wherever possible , in the new style. This probably also means splitting up the tests from the single file they are in now, radium-test.js.