For testing SNMP v1 and v2 credentials, the windows application SnmpB works. It is an open source tool, and can be downloaded from Source Forge
For testing SNMP v3, the tool is not all that helpful – a more powerful unix/linux based tool called "snmpwalk" can be used.
For Ubuntu, this is part of the snmp-mibs-downloader package
Usage Examples:
# login as a user with no authentication required snmpwalk -v 3 -l noauth -u noauthuser localhost # login as a user with Authentication required, but no Privacy snmpwalk -v 3 -l auth -u snmp3user -A Falcon99 localhost # Login as a user with authentication and privacy -- note that the -A (authentication) and -X (encryption) passwords can be different snmpwalk -v 3 -l auth -u snmp3user -A Falcon99 -X Falcon99 localhost