tests/libstore-support: avoid host configuration

setting a global like this is a hacky solution, but it works for now.

without this, unit tests try to use configuration under `/etc/nix/`.

Signed-off-by: Dusk Banks <me@bb010g.com>
Change-Id: Ic7966a67d52646818991646439225a7af20f011c

tests/unit/libstore-support/tests/libstore.hh

@@ -4,6 +4,7 @@
 #include <gtest/gtest.h>
 #include <gmock/gmock.h>
 
+#include "globals.hh"
 #include "store-api.hh"
 
 namespace nix {
@@ -11,6 +12,7 @@ namespace nix {
 class LibStoreTest : public ::testing::Test {
     public:
         static void SetUpTestSuite() {
+            settings.nixConfDir = "/dev/null"; // intentionally invalid path
             initLibStore();
         }