The syntax for sending a test syslog from a Cisco device depends on software version; here are the command syntaxes I've seen, including, where available, the option for setting syslog severity:
Most Cisco platforms, if running IOS 12.2(58) and higher:
send log [severity] [text to send]
Eg:
send log
send log This message will go to my syslog server.
send log 5 This message will go to my syslog server.
Most Cisco platforms, if running IOS 12.2(52) and lower:
send log [text to send]
Eg:
send log
send log This message will go to my syslog server.
ASR1000 running IOS-XE 03.01.00, which is sourced from IOS 15.0(1):
send log [severity [text to send]]
Eg:
send log
send log 5 This message will go to my syslog server.
ASR1000 running other IOS-XE versions (including 02.04.03 from IOS 12.2(33), 03.04.04 from IOS 15.1(3), 03.14.00 from IOS 15.5(1)):
send log [severity] [text to send]
Eg:
send log
send log This message will go to my syslog server.
send log 5 This message will go to my syslog server.
ASR9000 running IOS-XR 4.2.1 and higher:
log <text to send>
Eg:
log This message will go to my syslog server.
WS-C6513 running IOS 12.2(18): No equivalent command; you need to use another method to generate a syslog message. For example, the following should generate 5 syslogs (interface up, line protocol up, interface down, line protocol down, and configuration changed), depending on your logging settings. Leave out the 2 interface commands to generate just the one generic configuration-changed syslog.
config t
interface loopback601
no interface loopback601
end