Introduce usagef() that takes a printf-style format

diff --git a/t/t3414-rebase-preserve-onto.sh b/t/t3414-rebase-preserve-onto.sh
index 80019ee07212a553f97d5fd351f2ee9cfab93d9e..ee0a6cccfda832c62233d358f4933e9cd3ab2c8d 100755 (executable)
--- a/t/t3414-rebase-preserve-onto.sh
+++ b/t/t3414-rebase-preserve-onto.sh
@@ -10,7 +10,7 @@ aren'"'"'t on top of $ONTO, even if they are on top of $UPSTREAM.
 '
 . ./test-lib.sh
 
-. ../lib-rebase.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
 
 # Set up branches like this:
 # A1---B1---E1---F1---G1