So, this is about testing and test plans.
When you create them - and this applies equally for unit 10 (spreadsheets) and unit 3 (databases) you need sets of test data. That means data you want to use to test that your system works properly and check that it gives you the expected results.
You need to be really clear about the data you're going to use - that means I expect to see precisely what you're going to input - 10 in that box, Blue in that option and so on.
Now, the data needs to include 3 types:
- Normal - this is data which you would expect. Standard data that the system should accept without any problems
- Extreme - this is data at the extreme range of acceptable. You sometimes see this called 'boundary values'. You need to test each side of the boundary - so if a data value should accept values from 1-9 then I'd expect to see 9 and 10 being tested; if it has to be a maximum length then I'd expect testing at that length and one above the length and so on
- Erroneous - this is data which is clearly wrong - data which should never be accepted by the system. You want the system to reject this data. So, if I wanted a value 1-9 then I'd test things like 14, 473535, -1, 0, 4.5 and red.