t5730: introduce fetch command helper

Assembling a "raw" fetch command to be fed directly to "test-tool serve-v2"
is extracted into a test helper.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Kim Altintop <kim@eagain.st>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5703-upload-pack-ref-in-want.sh

@@ -40,6 +40,30 @@ write_command () {
 	fi
 }
 
+# Write a complete fetch command to stdout, suitable for use with `test-tool
+# pkt-line`. "want-ref", "want", and "have" lines are read from stdin.
+#
+# Examples:
+#
+# write_fetch_command <<-EOF
+# want-ref refs/heads/main
+# have $(git rev-parse a)
+# EOF
+#
+# write_fetch_command <<-EOF
+# want $(git rev-parse b)
+# have $(git rev-parse a)
+# EOF
+#
+write_fetch_command () {
+	write_command fetch &&
+	echo "0001" &&
+	echo "no-progress" &&
+	cat &&
+	echo "done" &&
+	echo "0000"
+}
+
 # c(o/foo) d(o/bar)
 #        \ /
 #         b   e(baz)  f(main)
@@ -77,15 +101,11 @@ test_expect_success 'config controls ref-in-want advertisement' '
 '
 
 test_expect_success 'invalid want-ref line' '
-	test-tool pkt-line pack >in <<-EOF &&
-	$(write_command fetch)
-	0001
-	no-progress
+	write_fetch_command >pkt <<-EOF &&
 	want-ref refs/heads/non-existent
-	done
-	0000
 	EOF
 
+	test-tool pkt-line pack <pkt >in &&
 	test_must_fail test-tool serve-v2 --stateless-rpc 2>out <in &&
 	grep "unknown ref" out
 '
@@ -97,16 +117,11 @@ test_expect_success 'basic want-ref' '
 	EOF
 	git rev-parse f >expected_commits &&
 
-	oid=$(git rev-parse a) &&
-	test-tool pkt-line pack >in <<-EOF &&
-	$(write_command fetch)
-	0001
-	no-progress
+	write_fetch_command >pkt <<-EOF &&
 	want-ref refs/heads/main
-	have $oid
-	done
-	0000
+	have $(git rev-parse a)
 	EOF
+	test-tool pkt-line pack <pkt >in &&
 
 	test-tool serve-v2 --stateless-rpc >out <in &&
 	check_output
@@ -121,17 +136,12 @@ test_expect_success 'multiple want-ref lines' '
 	EOF
 	git rev-parse c d >expected_commits &&
 
-	oid=$(git rev-parse b) &&
-	test-tool pkt-line pack >in <<-EOF &&
-	$(write_command fetch)
-	0001
-	no-progress
+	write_fetch_command >pkt <<-EOF &&
 	want-ref refs/heads/o/foo
 	want-ref refs/heads/o/bar
-	have $oid
-	done
-	0000
+	have $(git rev-parse b)
 	EOF
+	test-tool pkt-line pack <pkt >in &&
 
 	test-tool serve-v2 --stateless-rpc >out <in &&
 	check_output
@@ -144,16 +154,12 @@ test_expect_success 'mix want and want-ref' '
 	EOF
 	git rev-parse e f >expected_commits &&
 
-	test-tool pkt-line pack >in <<-EOF &&
-	$(write_command fetch)
-	0001
-	no-progress
+	write_fetch_command >pkt <<-EOF &&
 	want-ref refs/heads/main
 	want $(git rev-parse e)
 	have $(git rev-parse a)
-	done
-	0000
 	EOF
+	test-tool pkt-line pack <pkt >in &&
 
 	test-tool serve-v2 --stateless-rpc >out <in &&
 	check_output
@@ -166,16 +172,11 @@ test_expect_success 'want-ref with ref we already have commit for' '
 	EOF
 	>expected_commits &&
 
-	oid=$(git rev-parse c) &&
-	test-tool pkt-line pack >in <<-EOF &&
-	$(write_command fetch)
-	0001
-	no-progress
+	write_fetch_command >pkt <<-EOF &&
 	want-ref refs/heads/o/foo
-	have $oid
-	done
-	0000
+	have $(git rev-parse c)
 	EOF
+	test-tool pkt-line pack <pkt >in &&
 
 	test-tool serve-v2 --stateless-rpc >out <in &&
 	check_output