test_expect_success setup '
 
-       cat ../../COPYING >test &&
+       cat "$TEST_DIRECTORY"/../COPYING >test &&
        git add test &&
-       tr 'a-zA-Z' 'n-za-mN-ZA-M' <../../COPYING >test
+       tr \
+         "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" \
+         "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM" \
+         <"$TEST_DIRECTORY"/../COPYING >test
 
 '