HUnit testing with file dependent tests

Question

I have a lexer, and wish to test it against a set of known good test cases. These are held in a subdirectory ./test_src/ , and each has an extension testname .txt

What i'd like to do is get the paths to all relevant test cases:

getTestFiles :: IO [FilePath]
find always (extension ==? ".txt") "/path/to/test_src/"

and create a HUnit TestList containing HUnit TestCases each with an assertion created via a function along the lines of

testMyLexer :: IO FilePath -> Assertion

something along the lines of

myTest :: [IO FilePath] -> Test
myTest = TestList $ fmap TestCase $ fmap testMyLexer 

where I seem to be failng in my approach is that this seems to first require the follwoing function, and then mapping over its result:

unableToDoThis :: IO [FilePath] -> [IO FilePath]

I've a strong suspicion the approach I'm following is impossible, as it seems to require escaping the IO Monad, so what I'm asking is:

1. is this approach viable, if so what am I missing?
2. if not, how would you go about solving this problem? It must be pretty common to avoid hard coding in all test cases

Answer 1

Usually if you get wrapped IO a values in arguments then you're probably doing something wrong. Both testMyLexer and myTest can be pure, so instead of

testMyLexer :: IO FilePath -> Assertion
myTest :: [IO FilePath] -> Test

do

testMyLexer :: FilePath -> Assertion
myTest :: [FilePath] -> Test

Then it's just a matter of using bind from getTestFiles to extract your [FilePath] :

do
    files <- getTestFiles
    runTestTT $ myTest files