Adding test for node/index.js

Adding a test which verifies that and credentials have been initialized correctly when done so through index.js. The one thing I'm not sure about is whether I've created the node in the way that is intended. If I have then this pull request is ready to merge, if not then I can rework it.
I suggest rather than use `getCredentials` you test that `testnode.credentials` is defined and that `testnode.credentials.b`, `testnode.credentials.c` are defined and have the expected values.