Samba 4.6 verifies the ID mapping configuration. However, neither testparm reports an incorrect configuration, nor Winbindd fails to start if the upper end of the range is lower than the start. For example, the following configuration works
idmap config *:backend = tdb
idmap config *:range = 10001-15000
idmap config SAMDOM:backend = ad
idmap config SAMDOM:schema_mode = rfc2307
idmap config SAMDOM:range = 20000-10000
I think we should include this test, because the user might forgot to add a trailing "0" and accidentally wrote 10000 instead of 100000, such as in the previous example.