test: regression tests for n_d_status_string and n_d_get_path

These do not crash on a closed database, and we want to keep it that
way.

Start a new file of tests as T560-lib-error was starting to get unwieldy.

test/T562-lib-database.sh

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+test_description="error reporting for library"
+
+. $(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 <notmuch.h>
+#include <notmuch-test.h>
+int main (int argc, char** argv)
+{
+   notmuch_database_t *db;
+   notmuch_status_t stat;
+   char *msg = NULL;
+
+   stat = notmuch_database_open_verbose (argv[1], NOTMUCH_DATABASE_MODE_READ_WRITE, &db, &msg);
+   if (stat != NOTMUCH_STATUS_SUCCESS) {
+     fprintf (stderr, "error opening database: %d %s\n", 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
+
+test_begin_subtest "get status_string with closed db"
+cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR}
+    {
+        const char *str;
+        EXPECT0(notmuch_database_close (db));
+        str = notmuch_database_status_string (db);
+        printf("%d\n", str == NULL);
+    }
+EOF
+cat <<EOF > EXPECTED
+== stdout ==
+1
+== stderr ==
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
+test_begin_subtest "get path with closed db"
+cat c_head - c_tail <<'EOF' | test_C ${MAIL_DIR}
+    {
+        const char *path;
+        EXPECT0(notmuch_database_close (db));
+        path = notmuch_database_get_path (db);
+        printf("%s\n", path);
+    }
+EOF
+cat <<EOF > EXPECTED
+== stdout ==
+MAIL_DIR
+== stderr ==
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
+test_done