diff --git a/src/GA.hs b/src/GA.hs
index 7ff5702..69c3aed 100644
--- a/src/GA.hs
+++ b/src/GA.hs
@@ -183,6 +183,12 @@ prop_bestsBy_isBestsBy' k pop =
       b <- bestsBy' k fitness pop
       assert $ NE.toList a == b
 
+prop_bestsBy_lengths k pop =
+  k > 0 ==> monadicIO $ do
+    (bests, rest) <- bestsBy k fitness pop
+    assert
+      $ length bests == min k (length pop) && length bests + length rest == length pop
+
 {-|
 The @k@ worst individuals in the population.
 -}
diff --git a/src/Test.hs b/src/Test.hs
index e0a921d..a7fbe27 100644
--- a/src/Test.hs
+++ b/src/Test.hs
@@ -8,6 +8,6 @@ import qualified Seminar
 
 main :: IO ()
 main = do
-  _ <- Seminar.runTests
   _ <- GA.runTests
+  _ <- Seminar.runTests
   return ()