Test case creation tips 
Only create test modules for transactions which you know well.
Only call transactions by reference to a test module.
Only put one transaction in a test module.
Always use parameters to pass values to transactions.
Choose the parameters and screen sequence so as to make the test case as generally usable as possible.
Avoid creating new test cases when existing ones can be modified.
Always modify test cases so that they remain compatible.
Document all test cases.
Use existing test cases in other applications to use their transactions, requesting modifications if necessary.
Use variants to broaden the range of tests.