Add some the scaffolding for testing

As I attempt to habituate TDD, I should have some examples of tests to minimize
all friction preventing me from testing.

scratch/brilliant/shell.nix

@@ -3,6 +3,7 @@ let
 in pkgs.mkShell {
   buildInputs = with pkgs; [
     (haskellPackages.ghcWithPackages (hpkgs: with hpkgs; [
+      hspec
       optparse-applicative
     ]))
   ];