Update tests

**Bug:**

`api/notifications.js` called a non-existent function `next` if the server did not contain the ledger required to query transaction. Should have called function `async_callback`. Fixed

**Note:**

+ The unit tests in test/payments-test.js were commented out. Unit tests should exist separate to the functional tests. I figured it was safe to comment them out because they were minimal

+ I didn't rewrite the test titles in _payments-test.js as that would take a long time and I'm not sure if the tests will be useful in the future