t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that
lets developers run the test suite with a different default ref format
without impacting the ref format used by non-test Git invocations. This
is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same
thing for the repository's object format.

Adapt the setup of the `REFFILES` test prerequisite to be conditionally
set based on the default ref format.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/README

@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 

t/test-lib-functions.sh

@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {

t/test-lib.sh

@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 
@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL