tests: Fix FL_CACHE_DIR when system helper is compiled out

The tests assumed that a system installation always uses the XDG cache
location unless running as root. However, Flatpak only uses that cache
location when the system helper is available at both compile and run
time. [1]

Builds configured with -Dsystem_helper=disabled instead use the
repo-local cache directory [2], causing the tests to look for cached
summaries in the wrong location and fail.

[1]: 96ad6825f3/common/flatpak-dir.c (L4853-L4862)
[2]: 96ad6825f3/common/flatpak-dir.c (L4942-L4943)

tests/libtest.sh

@@ -136,13 +136,16 @@ if [ x${USE_SYSTEMDIR-} == xyes ] ; then
     export FL_DIR=${SYSTEMDIR}
     export U=
     export INVERT_U=--user
-    if [ x${UID} == x0 ] ; then
-        # If running as root (which happens on some build machines), the
-        # system-helper will not be used, and hence the fallback cache dir will
-        # be used in _flatpak_dir_ensure_repo().
-        export FL_CACHE_DIR=$FL_DIR/repo/tmp/cache
-    else
+    if [ x${HAVE_SYSTEM_HELPER-} == x1 ] && [ x${UID} != x0 ] ; then
+        # If system helper is compiled during build and will actually be
+        # used at runtime eg. UID != 0, Flatpak stores summary caches
+        # in the user's XDG cache directory
         export FL_CACHE_DIR=${XDG_CACHE_HOME}/flatpak/system-cache
+    else
+        # If the system helper is unavailable at build time, or it
+        # cannot be used eg. UID == 0 Flatpak uses the repo-local cache
+        # directory.
+        export FL_CACHE_DIR=$FL_DIR/repo/tmp/cache
     fi
 else
     export FL_DIR=${USERDIR}

tests/meson.build

@@ -31,6 +31,7 @@ tests_environment = {
   'FLATPAK_BWRAP' : env_flatpak_bwrap,
   'FLATPAK_DBUSPROXY' : env_flatpak_dbusproxy,
   'HAVE_SECCOMP' : libseccomp_dep.found() ? '1' : '0',
+  'HAVE_SYSTEM_HELPER' : build_system_helper ? '1' : '0',
 }
 
 tests_environment_prepend = {