what exactly do you test? there are many test options in cognos configuration.. if you test the top level, then it tests the entire configuration and not just the content store.. if you have not set up the mail server portion yet, then the test will appear to fail.
please post:
the exact error message when the test fails.
what db you are using (and version).
where you got the jdbc driver (if applicable)
Are you able to log into cognos connection? if so, i suspect either the jdbc driver is incorrect or the configuration is being tested from the top level.