Add edge case test for defaults in sum-of-multiples

Author: petemcfarlane

exercises/sum-of-multiples/example.hs

@@ -1,5 +1,6 @@
 module SumOfMultiples (sumOfMultiples) where
 
 sumOfMultiples :: [Int] -> Int -> Int
+sumOfMultiples [] upperBound = sumOfMultiples [3,5] upperBound
 sumOfMultiples targets upperBound = sum (filter f [1..upperBound-1])
   where f n = any ((==0) . mod n) targets

exercises/sum-of-multiples/sum-of-multiples_test.hs

@@ -25,6 +25,8 @@ sumOfMultiplesTests =
     23 @=? sumOfMultiples [3, 5] 10
   , testCase "1000" $
     233168 @=? sumOfMultiples [3, 5] 1000
+  , testCase "[7, 13, 17] 20" $
+    543 @=? sumOfMultiples [] 50
   , testCase "[7, 13, 17] 20" $
     51 @=? sumOfMultiples [7, 13, 17] 20
   , testCase "[4, 6] 15" $