A failure in a check step is not the same thing as an error. A failure simply means that the check/test did not pass. An error should be reserved for unexpected exceptions, the application under test...
A keyword test = code... just of a different format. So, what you will need to do is build into your keyword test the same sort of checks of for loops/while loops, etc, checking for whether or not a particular criteria is met within a time frame... if it is not met in the time frame, log message (error, warning, etc., custom priority, etc) indicating the failure to meet the conditions and report it. Then, "clean up" the situation and move on to the next part of the test. It's not a "unit test", it's just a matter of a well-designed automated test that a) tests what you need it to test b) accounts for potential anticipated fail points and c) handles "unexpected" scenarios and then log/document the results for human interpretation....