tests: Add ghcWithHoogle test

Author: rvl

test/snapshots/default.nix

@@ -1,19 +1,33 @@
-{ stdenv, haskellPackages }:
+{ stdenv, haskellPackages, snapshots }:
 
 with stdenv.lib;
 
+let
+  env = snapshots."lts-12.21".ghcWithHoogle
+    (ps: with ps; [ conduit conduit-extra resourcet ]);
+
+in
   stdenv.mkDerivation {
     name = "shell-for-test";
 
     buildCommand = ''
       ########################################################################
-      # test snapshot ghcWithHoogle
+      # test single component from haskellPackages
 
       printf "checking that the latest LTS snapshot has the lens package...\n" >& 2
       test -d ${haskellPackages.lens.components.library}
 
+      ########################################################################
+      # test snapshot ghcWithHoogle
+
+      printf "checking that the ghcWithPackages env has the package...\n" >& 2
+      ${env}/bin/ghc-pkg list | grep conduit
+
       touch $out
     '';
 
     meta.platforms = platforms.all;
-  }
+    passthru = {
+      inherit env;
+    };
+}