Split tests some more

Good for parallelism and easier reading.

tests/overlay-local-store/build-inner.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+set -eu -o pipefail
+
+set -x
+
+source common.sh
+
+storeDirs
+
+initLowerStore
+
+mountOverlayfs
+
+### Do a build in overlay store
+
+path=$(nix-build ../hermetic.nix --arg busybox $busybox --arg seed 2 --store "$storeB" --no-out-link)
+
+# Checking for path in lower layer (should fail)
+expect 1 stat $(toRealPath "$storeA/nix/store" "$path")
+
+# Checking for path in upper layer
+stat $(toRealPath "$storeBTop" "$path")
+
+# Verifying path in overlay store
+nix-store --verify-path --store "$storeB" "$path"