test/tag: add test for updating during batch tag operations

This clarifies that the breakage seen with Xapian 1.4.6 does not have
to do with "funny" tags.

This test is "known broken", but only with xapian 1.4.6, and there's
curently no convenient way to mark that.

test/T150-tagging.sh

@@ -130,6 +130,19 @@ EOF
 test_expect_equal_file batch_removeall.expected OUTPUT
 rm batch_removeall.expected
 
+test_begin_subtest "--batch, dependence on previous line"
+notmuch dump --format=batch-tag > backup.tags
+notmuch tag --batch<<EOF
++trigger -- One
++second_tag -- tag:trigger
+EOF
+NOTMUCH_DUMP_TAGS tag:second_tag > OUTPUT
+notmuch restore --format=batch-tag < backup.tags
+cat <<EOF >EXPECTED
++inbox +second_tag +tag5 +trigger +unread -- id:msg-001@notmuch-test-suite
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
 test_begin_subtest "--batch, blank lines and comments"
 notmuch dump | sort > EXPECTED
 notmuch tag --batch <<EOF