test-lib: Introduce test_chmod and use it instead of update-index --chmod

This function replaces sequences of 'chmod +x' and 'git update-index
--chmod=+x' in the test suite, whose purpose is to help filesystems
that need core.filemode=false. Two places where only 'chmod +x' was used
we also use this new function.

The function calls 'git update-index --chmod' without checking
core.filemode (unlike some of the call sites did). We do this because the
call sites *expect* that the executable bit ends up in the index (ie. it
is not the purpose of the call sites to *test* whether git treats
'chmod +x' and 'update-index --chmod=+x' correctly). Therefore, on
filesystems with core.filemode=true the 'git update-index --chmod' is a
no-op.

The function uses --add with update-index to help one call site in
t6031-merge-recursive. It makes no difference for the other callers.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>

t/test-lib.sh

@@ -238,6 +238,15 @@ test_merge () {
 	git tag "$1"
 }
 
+# This function helps systems where core.filemode=false is set.
+# Use it instead of plain 'chmod +x' to set or unset the executable bit
+# of a file in the working directory and add it to the index.
+
+test_chmod () {
+	chmod "$@" &&
+	git update-index --add "--chmod=$@"
+}
+
 # You are not expected to call test_ok_ and test_failure_ directly, use
 # the text_expect_* functions instead.