# How to identify and justify how many test cases is enough when you have a potentially huge number of combinations?

I'm working on a form builder project.

Users can drag and drop elements to build questionnaires.

If we simplify and say there is only 3 form elements that can be used:

1. Numeric answer, with configurable number of decimal points allowed 0 to 12
2. Multiple choice, click 1 radio button
3. yes or no, click 1 radio button

My maths says this gives us 3 forms with 1 control, 3 with 2 and 1 with 3.

We can then say that the numeric has 3 test configuration , (0,2 and 12 decimal points - the min/max plus happy common value, debatable but hopefully sensible).

Which gives us 5 forms with 1 control, 5 with 2 and 1 with 3.

However, one can have multiple of each control on a page. Lets say a page is limited to 100 controls.

It makes sense to me to test all of the above scenarios but then also where each control is duplicated - to see if having e.g. 2 numeric controls somehow interact with unintended consequences.

Beyond having 2 of each control - is there value in having 3 of each or 4 of each? How do I pick a number and justify it? I can't imagine if having 2 of each control on a page in each configuration doesn't cause any interactions, that having 3 or 4 or 9 - suddenly would do so?