Being very general about the topic, take a look at some of the articles, which give a fair idea behind the decision to automate a testcase. Testing Hotlist
<UL TYPE=SQUARE><LI>When should a test be automated<LI>Seven steps to test automation<LI>Classic testing mistakes[/list]You will find other articles on the same topic which will set you off on the right foot.
One fairly simple way to determine this is to
rank your test cases in descending order of
the combination of
1) ease of automation
2) liklihood of finding a problem
This will naturally lead you to automate the
"best bang for the buck" test cases first.
One important note is that "ease of automation" includes"
- ease of creating the initial test case
- ease of maintaining the test case
- ease of isolating the failure cause of the
test case when it fails
Many people make the mistake of focusing on
the 1st item and de-emphasizing or ignoring
the last two.
Test Architect (Demolition Man)
Testability = 1/complexity