Testing Tip #1 - Boundary testing business objects

When testing business objects, for example an object that represents a Person or a Customer, you often have a minimum set of data requirements. I.e. a customer must have a last name. As well as having a set of optional data attributes (first name, date of birth, gender, etc).

To provide full test coverage you would mathematically need to provide N factorial minus M factorial combinations where N is the number of attributes and M is the number of mandatory attributes. I don't think I have ever had enough time to test that much, incredibly boring, testing and nor would I, had I.

In my experience the best pass through is to look at the two bounds. The minimum set where you specify the object with the bare minimum of attributes, the mandatory attributes, and each of these attributes has as little data as possible. In our customer example this would be a last name that is one single character in length.

The next test case would include every single attribute populated to it's maximum extent. So if you have a twenty character first name you specify all twenty characters. I document this as my all set.

These two test cases have been enough for every system I've tested. Using them you can prove every attribute being supplied and every attribute being absent, or supplied to their bare minimum allowed.


I don't include out-of-bounds testing here. That is, I don't check for 21 character first name objects, nor do I test for zero length last names. That specific boundary testing, I document as separate tests against the user interface. This achieves two things. Firstly, my test cases are granular and relate to a specific business requirement. This then means that defects raised are very specific and generally easier to track down. Secondly it cuts the amount of testing I have to do to what is more than likely going to cause defects.

Additional:
If you have more complex data types. For instance, if there is a business rule that states that attribute-x is only provided when attribute-z is set. Then that specific combination is already covered by your all set (attribute-z is set) and your minimum set (attribute-z is not set). I would additionally include test cases to ensure that any user interface validation of these attributes occurs.