Write unit tests for `parse-events`

[daveyarwood]

parse-events (implemented by @wcerfgba in #4) uses the Alda v2 alda parse events output to produce alda-clj event records from Alda input (which could take the form of alda-clj event records and/or strings of Alda code, since ->str is used internally by parse-events)

It would be nice to have unit tests for this, especially since they would be easy to write.

To test:

• Equivalence of strings of Alda code and the result of applying parse-events and then ->str

  • (= "@foo" (-> "@foo" parse-events ->str))

• Equivalence of alda-clj events and the result of applying parse-events to them.

  • (= [(->AtMarker "foo")] (parse-events "@foo"))