[test] show diff when ast's are different

package.yaml

@@ -50,6 +50,8 @@ dependencies:
 # when running the tests. Is there a better solution?
 - tasty
 - tasty-hunit
+- Diff == 0.4.*
+- pretty-show == 1.10.*
 
 # TODO organize this
 ghc-options:
@@ -89,7 +91,6 @@ executables:
     dependencies:
     - minijuvix
     - optparse-applicative == 0.17.*
-    - pretty-show == 1.10.*
     verbatim:
       default-language: GHC2021
 

test/Scope/Positive.hs

@@ -5,6 +5,9 @@ import qualified MiniJuvix.Syntax.Concrete.Scoped.Pretty.Text as M
 import qualified MiniJuvix.Syntax.Concrete.Scoped.Scoper as M
 import MiniJuvix.Syntax.Concrete.Scoped.Utils
 import qualified Data.HashMap.Strict as HashMap
+import Text.Show.Pretty hiding (Html)
+import Data.Algorithm.Diff
+import Data.Algorithm.DiffOutput
 
 
 data PosTest = PosTest {
@@ -44,11 +47,22 @@ testDescr PosTest {..} = TestDescr {
     s' <- fromRightIO' printErrorAnsi $ return (M.scopeCheck1Pure fs "." p')
 
     step "Checks"
-    assertBool "check: scope . parse . pretty . scope . parse = scope . parse" (s == s')
-    assertBool "check: parse . pretty . scope . parse = parse" (p == p')
-    assertBool "check: parse . pretty . parse = parse" (p == parsedPretty')
+    assertEqDiff "check: scope . parse . pretty . scope . parse = scope . parse" s s'
+    assertEqDiff "check: parse . pretty . scope . parse = parse" p p'
+    assertEqDiff "check: parse . pretty . parse = parse" p parsedPretty'
   }
 
+assertEqDiff :: (Eq a, Show a) => String -> a -> a -> Assertion
+assertEqDiff msg a b
+  | a == b = return ()
+  | otherwise = do
+      putStrLn (pack $ ppDiff (getGroupedDiff pa pb))
+      putStrLn "End diff"
+      fail msg
+    where
+    pa = lines $ ppShow a
+    pb = lines $ ppShow b
+
 allTests :: TestTree
 allTests = testGroup "Scope positive tests"
   (map (mkTest . testDescr) tests)