[PATCH v2 2/3] t/t6300: introduce test_bad_atom

[Kousik Sanagavarapu <five231003@gmail.com>]

Introduce a new function "test_bad_atom", which is similar to
"test_atom()" but should be used to check whether the correct error
message is shown on stderr.

Like "test_atom", the new function takes three arguments. The three
arguments specify the ref, the format and the expected error message
respectively, with an optional fourth argument for tweaking
"test_expect_*" (which is by default "success").

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com>
---
 t/t6300-for-each-ref.sh | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 7ba9949376..e4ec2926d6 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -271,6 +271,30 @@ test_expect_success 'arguments to %(objectname:short=) must be positive integers
 	test_must_fail git for-each-ref --format="%(objectname:short=foo)"
 '
 
+test_bad_atom () {
+	case "$1" in
+	head) ref=refs/heads/main ;;
+	 tag) ref=refs/tags/testtag ;;
+	 sym) ref=refs/heads/sym ;;
+	   *) ref=$1 ;;
+	esac
+	format=$2
+	test_do=test_expect_${4:-success}
+
+	printf '%s\n' "$3" >expect
+	$test_do $PREREQ "err basic atom: $ref $format" '
+		test_must_fail git for-each-ref \
+			--format="%($format)" "$ref" 2>error &&
+		test_cmp expect error
+	'
+}
+
+test_bad_atom head 'authoremail:foo' \
+	'fatal: unrecognized %(authoremail) argument: foo'
+
+test_bad_atom tag 'taggeremail:localpart trim' \
+	'fatal: unrecognized %(taggeremail) argument: localpart trim'
+
 test_date () {
 	f=$1 &&
 	committer_date=$2 &&
-- 
2.42.0.273.ge948a9aaf4