verboseCheck in QuickCheck 2?

Question

The function verboseCheck from QuickCheck 1 seems to be absent in QuickCheck 2 (or at least, I can't find it). Is there any other way to show which values are used during testing?

Answer 1

I took a look at sources, and it seems that Args were refactored, configEvery is no longer there, and thus you are not able to print all test values without patching QuichCheck sources

Answer 2

Yes, this seems to be a functionality regression with respect to QuickCheck 1.

You can work around it by annotating your properties with a Debug.Trace.trace statement, however. Something like:

import Debug.Trace

prop_eq xs = traceShow xs $ 
   xs == reverse (reverse xs)

Answer 3

The sample function is also useful:

Prelude Test.QuickCheck
ghci> sample (arbitrary :: Gen String)
""
")\223"
"(\227\&5F"
"\DC1"
"\136'\140\180\FS"
"K\DC2\NUL\CAN\253Q"
"\DC4\f\184&.\DC3\159\&1I\160j\147"
....

This way, it's easy to play with your Arbitrary instances, and make sure they generate what you think they generate.

Answer 4

I've been happy with

import Debug.Trace
verboseCheck prop = quickCheck (\input -> traceShow input $ prop input)