GIT_TEST_PRELOAD_INDEX=<boolean> exercises the preload-index code path
by overriding the minimum number of cache entries required per thread.
-GIT_TEST_STASH_USE_BUILTIN=<boolean>, when false, disables the
-built-in version of git-stash. See 'stash.useBuiltin' in
-git-config(1).
-
GIT_TEST_ADD_I_USE_BUILTIN=<boolean>, when true, enables the
built-in version of git add -i. See 'add.interactive.useBuiltin' in
git-config(1).