Deflake tests

 - no palindromic dates
 - no digits in arbitrary bytestrings

test/Test/Warden/Arbitrary.hs

@@ -11,10 +11,11 @@ import qualified Data.ByteString.Lazy as BL
 import           Data.Char
 import           Data.Csv
 import qualified Data.Set as S
-import           Data.List (nub)
+import           Data.List ((\\), nub)
 import qualified Data.List as L
 import           Data.List.NonEmpty (NonEmpty)
 import qualified Data.List.NonEmpty as NE
+import           Data.String (String)
 import qualified Data.Text as T
 import           Data.Text.Encoding (decodeUtf8, decodeUtf8', encodeUtf8)
 import           Data.Time.Calendar (Day(..))
@@ -807,34 +808,45 @@ genSensibleDateTime = do
 renderedDate :: Gen BS.ByteString
 renderedDate = do
   dt <- genSensibleDateTime
-  render <- frequency [(1, renderNoSeparator), (9, renderSeparator)]
+  render <- frequency [(1, renderDateNoSeparator), (9, renderDateSeparator)]
   pure . BSC.pack $ render dt
-  where
-    renderNoSeparator = do
-      tp <- timePart
-      pure (formatTime defaultTimeLocale ("%Y%m%d" <> tp))
-
-    renderSeparator = do
-      tp <- timePart
-      sep <- elements ["-", ".", "/"]
-      pure (formatTime defaultTimeLocale ((concat ["%Y", sep, "%m", sep, "%d"]) <> tp))
-
-    timePart = elements [
-        ""
-      , "%H%M"
-      , "%H:%M"
-      , "%H%M%S"
-      , "%H:%M:%S"
-      , "T%H:%M:%SZ"
-      ]
+
+renderDateNoSeparator :: Gen (UTCTime -> String)
+renderDateNoSeparator = do
+  tp <- timePart
+  pure (formatTime defaultTimeLocale ("%Y%m%d" <> tp))
+
+renderDateSeparator :: Gen (UTCTime -> String)
+renderDateSeparator = do
+  tp <- timePart
+  sep <- elements ["-", ".", "/"]
+  pure (formatTime defaultTimeLocale ((concat ["%Y", sep, "%m", sep, "%d"]) <> tp))
+
+timePart :: Gen String
+timePart = elements [
+    ""
+  , "%H%M"
+  , "%H:%M"
+  , "%H%M%S"
+  , "%H:%M:%S"
+  , "T%H:%M:%SZ"
+  ]
 
 
 renderedNonDate :: Gen BS.ByteString
 renderedNonDate = do
-  x <- fmap BS.pack $ listOf1 arbitrary
+  x <- fmap BS.pack $ listOf1 noDigits
   dt <- renderedDate
   oneof [
       pure $ x <> dt
-    , pure $ BS.reverse dt
+    , reversed
     , encodeUtf8 <$> elements muppets
     ]
+  where
+    reversed = do
+      dt <- genSensibleDateTime
+      render <- renderDateSeparator
+      pure . BSC.pack . reverse $ render dt
+
+    noDigits =
+      elements $ [0x00..0xff] \\ [0x30..0x39]