How do you test results of formulas ?

[T Mark]

I'm happily generating spreadsheets with axlsx (thanks Randy and all!).

My spreadsheets contain a number of worksheets which calculate values using a host of formulas and lokoups.

I am, however, late to the testing party.  I'm trying to correct this, but can't seem to figure out how such spreadsheets would be tested - it would require evaluation at the spreadsheet level, which would seem to be a pretty big task.  I couldn't seem to find any tests which test this part of the functionality.  Even though I recognize that the functionality actually lies beyond axlsx.... but if what we really care about are the values that end up being displayed in the spreadsheet, how do we validate those ? 

So - is it possible to run tests on calculations performed in formulas which are themselves generated by axlsx ?  Or are we limited to testing the formulas that get put into those spreadsheets ?

thanks !