tests: use test_write_lines() to generate line-oriented output

Take advantage of test_write_lines() to generate line-oriented output
rather than using for-loops or a series of `echo` commands. Not only is
test_write_lines() a natural fit for such a task, but there is less
opportunity for a broken &&-chain.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7501-commit-basic-functionality.sh

@@ -667,10 +667,7 @@ test_expect_success 'amend can copy notes' '
 
 test_expect_success 'commit a file whose name is a dash' '
 	git reset --hard &&
-	for i in 1 2 3 4 5
-	do
-		echo $i
-	done >./- &&
+	test_write_lines 1 2 3 4 5 >./- &&
 	git add ./- &&
 	test_tick &&
 	git commit -m "add dash" >output </dev/null &&