Expose discoverPrefix to find prefixed properties

[ruhatch]

We are using this change to have specific sets of properties, for example golden tests, with their own prefix.

[moodmosaic]

Don't you want to have different tests in separate groups instead? Because Group might be all you need, since it's a named collection of property tests:

-- | A named collection of property tests.
--
data Group =
  Group {
      groupName :: !GroupName
    , groupProperties :: ![(PropertyName, Property)]
    }

Or, with TH, you can semantically group different tests in separate modules, and just do something like

results <- sequence [
    Test.Module.A.tests
  , Test.Module.B.tests
  , Test.Module.C.tests
  ]

unless (and results) $
  exitFailure

Hypothetically, A is your golden tests, B is your foo tests, and C is your bar tests, and so on.

[jacobstanley]

This is a nice change, thanks for the PR.