test: add known broken test for notmuch_tags_valid (NULL)

This should return false, but currently segfaults.

Start a new file for tags library API related tests. This is maybe
overkill, but new C boilerplate which doesn't corrupt the database is
needed anyway.

test/T560-lib-error.sh

@@ -274,24 +274,6 @@ EOF
 test_expect_equal_file EXPECTED OUTPUT.clean
 restore_database
 
-backup_database
-test_begin_subtest "Xapian exception getting tags"
-cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR} ${POSTLIST_PATH}
-   {
-       notmuch_tags_t *tags = NULL;
-       tags = notmuch_database_get_all_tags (db);
-       stat = (tags == NULL);
-   }
-EOF
-sed 's/^\(A Xapian exception [^:]*\):.*$/\1/' < OUTPUT > OUTPUT.clean
-cat <<'EOF' >EXPECTED
-== stdout ==
-== stderr ==
-A Xapian exception occurred getting tags
-EOF
-test_expect_equal_file EXPECTED OUTPUT.clean
-restore_database
-
 backup_database
 test_begin_subtest "Xapian exception creating directory"
 cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR} ${POSTLIST_PATH}

test/T565-lib-tags.sh

@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+test_description="API tests for tags"
+
+. $(dirname "$0")/test-lib.sh || exit 1
+
+add_email_corpus
+
+test_begin_subtest "building database"
+test_expect_success "NOTMUCH_NEW"
+
+cat <<EOF > c_head
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <talloc.h>
+#include <notmuch.h>
+
+int main (int argc, char** argv)
+{
+   notmuch_database_t *db;
+   notmuch_status_t stat;
+   char *path;
+   char *msg = NULL;
+   int fd;
+
+   stat = notmuch_database_open_with_config (argv[1],
+					      NOTMUCH_DATABASE_MODE_READ_WRITE,
+					      NULL, NULL, &db, &msg);
+   if (stat != NOTMUCH_STATUS_SUCCESS) {
+     fprintf (stderr, "error opening database\n%s\n%s\n", notmuch_status_to_string (stat), msg ? msg : "");
+     exit (1);
+   }
+EOF
+cat <<'EOF' > c_tail
+   if (stat) {
+       const char *stat_str = notmuch_database_status_string (db);
+       if (stat_str)
+	   fputs (stat_str, stderr);
+    }
+
+}
+EOF
+
+POSTLIST_PATH=(${MAIL_DIR}/.notmuch/xapian/postlist.*)
+
+backup_database
+test_begin_subtest "Xapian exception getting tags"
+cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR} ${POSTLIST_PATH}
+   {
+      notmuch_tags_t *tags = NULL;
+      fd = open(argv[2],O_WRONLY|O_TRUNC);
+      if (fd < 0) {
+	  fprintf (stderr, "error opening %s\n", argv[1]);
+	  exit (1);
+       }
+       tags = notmuch_database_get_all_tags (db);
+       stat = (tags == NULL);
+   }
+EOF
+sed 's/^\(A Xapian exception [^:]*\):.*$/\1/' < OUTPUT > OUTPUT.clean
+cat <<'EOF' >EXPECTED
+== stdout ==
+== stderr ==
+A Xapian exception occurred getting tags
+EOF
+test_expect_equal_file EXPECTED OUTPUT.clean
+restore_database
+
+test_begin_subtest "NULL tags are not valid"
+test_subtest_known_broken
+cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR}
+   {
+       notmuch_bool_t valid = TRUE;
+       valid = notmuch_tags_valid (NULL);
+       fprintf(stdout, "valid = %d\n", valid);
+   }
+EOF
+cat <<'EOF' >EXPECTED
+== stdout ==
+valid = 0
+== stderr ==
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
+test_done