yq: Add test

nixos/tests/yq.nix

@@ -0,0 +1,12 @@
+import ./make-test-python.nix ({ pkgs, ... }: {
+  name = "yq";
+  meta = with pkgs.stdenv.lib.maintainers; { maintainers = [ nequissimus ]; };
+
+  nodes.yq = { pkgs, ... }: { environment.systemPackages = with pkgs; [ jq yq ]; };
+
+  testScript = ''
+    assert "hello:\n  foo: bar\n" in yq.succeed(
+        'echo \'{"hello":{"foo":"bar"}}\' | yq -y .'
+    )
+  '';
+})