chore(yants): Move tests into subfolder & add to CI builds

nix/yants/.skip-subtree

@@ -1 +0,0 @@
-Yants subtree contains no further derivations.

nix/yants/README.md

@@ -1,8 +1,6 @@
 yants
 =====
 
-[![Build Status](https://travis-ci.org/tazjin/yants.svg?branch=master)](https://travis-ci.org/tazjin/yants)
-
 This is a tiny type-checker for data in Nix, written in Nix.
 
 # Features

nix/yants/tests/default.nix

@@ -1,5 +1,7 @@
+{ pkgs, ... }:
+
 with builtins;
-with (import ./default.nix {});
+with pkgs.nix.yants;
 
 # Note: Derivations are not included in the tests below as they cause
 # issues with deepSeq.
@@ -89,4 +91,4 @@ deepSeq rec {
     (struct { a = int; b = option string; })
     (sum { a = int; b = option string; })
   ];
-} "All tests passed!\n"
+} (pkgs.writeText "yants-tests" "All tests passed!")