test: nest sample tests as fixtures in real tests

also use new test helpers

lib/lib_test.nix

@@ -1,44 +0,0 @@
-{
-  pkgs,
-  lib,
-  ...
-}: let
-  ntlib = import ./. {inherit pkgs lib;};
-in {
-  suites."Lib Tests".tests = [
-    {
-      name = "autodiscovery";
-      type = "script";
-      script = let
-        actual = builtins.toFile "actual" (builtins.toJSON (ntlib.autodiscover {
-          dir = ./.;
-        }));
-      in
-        # sh
-        ''
-          export PATH="${pkgs.gnugrep}/bin"
-          grep -q lib_test.nix ${actual}
-          grep -q "\"base\":\"/nix/store/.*-source/lib/" ${actual}
-        '';
-    }
-    {
-      name = "binary";
-      type = "script";
-      script = let
-        binary =
-          (ntlib.mkBinary {
-            nixtests = "stub";
-            extraParams = "--pure";
-          })
-          + "/bin/nixtests:run";
-      in
-        # sh
-        ''
-          export PATH="${pkgs.gnugrep}/bin"
-          grep -q nixtest ${binary}
-          grep -q -- "--pure" ${binary}
-          grep -q -- "--tests=stub" ${binary}
-        '';
-    }
-  ];
-}