t5701: add setup test to remove side-effect dependency

Currently, the "test capability advertisement" test creates some files
with expected content which are used by other tests below it.

To remove that side-effect from this test, let's split up part of
it into a "setup"-type test which creates the files with expected content
which gets reused by multiple tests. This will be useful in a following
commit.

Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Usman Akinyemi <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Unique-Usman

t/t5701-git-serve.sh

@@ -7,22 +7,28 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
-test_expect_success 'test capability advertisement' '
+test_expect_success 'setup to generate files with expected content' '
+	printf "agent=git/%s\n" "$(git version | cut -d" " -f3)" >agent_capability &&
+
 	test_oid_cache <<-EOF &&
 	wrong_algo sha1:sha256
 	wrong_algo sha256:sha1
 	EOF
+
 	cat >expect.base <<-EOF &&
 	version 2
-	agent=git/$(git version | cut -d" " -f3)
+	$(cat agent_capability)
 	ls-refs=unborn
 	fetch=shallow wait-for-done
 	server-option
 	object-format=$(test_oid algo)
 	EOF
-	cat >expect.trailer <<-EOF &&
+	cat >expect.trailer <<-EOF
 	0000
 	EOF
+'
+
+test_expect_success 'test capability advertisement' '
 	cat expect.base expect.trailer >expect &&
 
 	GIT_TEST_SIDEBAND_ALL=0 test-tool serve-v2 \