Salesforce recommends that you write tests for the following:
- Single action
- Test to verify that a single record produces the correct, expected
result.
- Bulk actions
- Any Apex code, whether a trigger, a class or an extension, may be invoked
for 1 to 200 records. You must test not only the single record case,
but the bulk cases as well.
- Positive behavior
- Test to verify that the expected behavior occurs through every
expected permutation, that is, that the user filled out everything
correctly and did not go past the limits.
- Negative behavior
- There are likely limits to your applications, such as not being
able to add a future date, not being able to specify a negative amount,
and so on. You must test for the negative case and verify that the
error messages are correctly produced as well as for the positive,
within the limits cases.
- Restricted user
- Test whether a user with restricted access to the sObjects used
in your code sees the expected behavior. That is, whether they can
run the code or receive error messages.
For examples of these types of tests, see Testing Example.