[PATCH] test: add known broken test for duplicate thread-id terms

[David Bremner <david@tethera.net>]

According to my bijection, this bug has been present since commit
411675a6ce in 2017. It is apparently harmless for regular use, but
does make notmuch crash when compiled with -DDEBUG_DATABASE_SANITY.
---
 test/T670-duplicate-mid.sh | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/test/T670-duplicate-mid.sh b/test/T670-duplicate-mid.sh
index 4e5672ab..3fd59ca5 100755
--- a/test/T670-duplicate-mid.sh
+++ b/test/T670-duplicate-mid.sh
@@ -2,10 +2,27 @@
 test_description="duplicate message ids"
 . $(dirname "$0")/test-lib.sh || exit 1
 
+test_require_external_prereq xapian-delve
+
 add_message '[id]="duplicate"' '[subject]="message 1" [filename]=copy1'
 add_message '[id]="duplicate"' '[subject]="message 2" [filename]=copy2'
 
 add_message '[id]="duplicate"' '[subject]="message 0" [filename]=copy0'
+
+test_begin_subtest 'at most 1 thread-id per xapian document'
+test_subtest_known_broken
+db=${MAIL_DIR}/.notmuch/xapian
+cp /dev/null OUTPUT.raw
+for doc in $(xapian-delve -1 -t '' "$db" | grep '^[1-9]'); do
+    xapian-delve -1 -r "$doc"  "$db" | grep '^G' | wc -l >> OUTPUT.raw
+done
+sort -u < OUTPUT.raw > OUTPUT
+cat <<EOF > EXPECTED
+0
+1
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
 test_begin_subtest 'search: first indexed subject preserved'
 cat <<EOF > EXPECTED
 thread:XXX   2001-01-05 [1/1(3)] Notmuch Test Suite; message 1 (inbox unread)
-- 
2.30.2