Implement simple test for path-fetcher setting a correct lastModifiedDate

Co-authored-by: Théophane Hufschmitt <7226587+thufschmitt@users.noreply.github.com>

tests/fetchPath.sh

@@ -0,0 +1,6 @@
+source common.sh
+
+touch foo -t 222211111111
+# We only check whether 2222-11-1* **:**:** is the last modified date since
+# `lastModified` is transformed into UTC in `builtins.fetchTarball`.
+[[ "$(nix eval --impure --raw --expr "(builtins.fetchTree \"path://$PWD/foo\").lastModifiedDate")" =~ 2222111.* ]]

tests/local.mk

@@ -21,6 +21,7 @@ nix_tests = \
   tarball.sh \
   fetchGit.sh \
   fetchurl.sh \
+  fetchPath.sh \
   simple.sh \
   referrers.sh \
   optimise-store.sh \