my $mm = PublicInbox::Msgmap->new_file($full, 1);
is($mm->mid_set(1234, 'a@example.com'), 1, 'mid_set once OK');
ok(0 == $mm->mid_set(1234, 'a@example.com'), 'mid_set not idempotent');
my $mm = PublicInbox::Msgmap->new_file($full, 1);
is($mm->mid_set(1234, 'a@example.com'), 1, 'mid_set once OK');
ok(0 == $mm->mid_set(1234, 'a@example.com'), 'mid_set not idempotent');