tests: use 'test_must_be_empty' instead of 'test_cmp <empty> <out>'

diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 9e0d31700e0cf8228e0093f3166ec830a5816ba4..0fef49954f0b89c6f7532af24452e25805ddbe7b 100755 (executable)
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -174,7 +174,7 @@ test_expect_success 'submodule update does not fetch already present commits' '
          git submodule update > ../actual 2> ../actual.err
        ) &&
        test_i18ncmp expected actual &&
-       ! test -s actual.err
+       test_must_be_empty actual.err
 '
 
 test_expect_success 'submodule update should fail due to local changes' '