making it a bit easier to run individual tests in Doc.hs

[bbarker]

Overview

Previously, running e.g. stack test --fast unison-syntax --ta "DocParser.Hello"

Would result in:

Randomness seed for this run is 5876492311547008607
Raw test output to follow ...
------------------------------------------------------------
------------------------------------------------------------


😶  hmm ... no test results recorded
Tip: use `ok`, `expect`, or `crash` to record results
Tip: if running via `runOnly` or `rerunOnly`, check for typos

Now with this change we get:

🦄  DocParser.Hello.# Hello
🦄  DocParser.HelloAgain.# Hello
## Again

🦄  DocParser.HelloAgain.## Hello
# Again

I'm not sure this is the best solution, but maybe it is something to start with.