    it "calculates the square of an arbitrary integer" $
      property $ \(n :: Integer) -> square n == n * n
    it "calculates the square of an arbitrary double" $
      property $ \(n :: Double) -> square n == n * n
  describe "ggT" $ do
    it "calculates the gcd of 15 and 10" $
      ggT 15 10 `shouldBe` 5
    it "calculates the gcd of two arbitrary integer" $
      property $ \(a :: Integer) (b  :: Integer) -> ggT a b == gcd a b