t1092: update a write-tree test

* 'on all' in the title of the test 'write-tree on all' was unclear;
remove it.

* Add a baseline 'test_all_match git write-tree' before making any
changes to the index, providing a reference point for the 'write-tree'
prior to any modifications.

* Add a comparison of the output of 'git status --porcelain=v2' to test
the working tree after 'write-tree' exits.

* Ensure SKIP_WORKTREE files weren't materialized on disk by using
"test_path_is_missing".

Signed-off-by: Shuqi Liang <cheskaqiqi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1092-sparse-checkout-compatibility.sh

diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 0c78481..3aa6356 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -2080,22 +2080,32 @@
 	test_cmp actual expect
 '
 
-test_expect_success 'write-tree on all' '
+test_expect_success 'write-tree' '
 	init_repos &&
 
+	test_all_match git write-tree &&
+
 	write_script edit-contents <<-\EOF &&
 	echo text >>"$1"
 	EOF
 
+	# make a change inside the sparse cone
 	run_on_all ../edit-contents deep/a &&
-	run_on_all git update-index deep/a &&
+	test_all_match git update-index deep/a &&
 	test_all_match git write-tree &&
+	test_all_match git status --porcelain=v2 &&
 
+	# make a change outside the sparse cone
 	run_on_all mkdir -p folder1 &&
 	run_on_all cp a folder1/a &&
 	run_on_all ../edit-contents folder1/a &&
-	run_on_all git update-index folder1/a &&
-	test_all_match git write-tree
+	test_all_match git update-index folder1/a &&
+	test_all_match git write-tree &&
+	test_all_match git status --porcelain=v2 &&
+
+	# check that SKIP_WORKTREE files are not materialized
+	test_path_is_missing sparse-checkout/folder2/a &&
+	test_path_is_missing sparse-index/folder2/a
 '
 
 test_expect_success 'sparse-index is not expanded: write-tree' '