Add test corresponding to builtins.placeholder "foo" in layer above

We were hashing correctly, but base32-ing wrong.

Author: Ericson2314

hnix-store-core/tests/Hash.hs

@@ -31,6 +31,10 @@ spec_hash = do
 
   describe "hashing parity with nix-store" $ do
 
+    it "produces (base32 . sha256) of \"nix-output:foo\" the same as Nix does at the moment for placeholder \"foo\"" $
+      shouldBe (printAsBase32 (hash @SHA256 "nix-output:foo"))
+               "1x0ymrsy7yr7i9wdsqy9khmzc1yy7nvxw6rdp72yzn50285s67j5"
+
     it "produces (base32 . sha1) of \"Hello World\" the same as the thesis" $
       shouldBe (printAsBase32 (hash @SHA1 "Hello World"))
                "s23c9fs0v32pf6bhmcph5rbqsyl5ak8a"