Testing a Revamped Budget File

The past week I've been reviewing a revamped budget file. The budget file is totally revamped which means extensive testing is required. I was able to design an automated checking of whether cells are appropriately locked (or unlocked) using the CELL("protect", ref) function. I also have a user defined function CellFormula (a macro) that shows the cell formula as text but I haven't yet successfully designed a test using this function. Now I'm struggling with actually testing the file and I'm daunted by the task. My boss did ask another person to help with the testing but I'm thinking we might need to divvy up the job.

It's very tedious filling out the blanks to see if the formulas work and I don't do that kind of stuff very well. Do I peruse every row's formulas to make sure it is set up properly? What kind of tests should I do? How do I fill up the cells without it taking a long time? How do I know if the numbers are reasonable? When I get into the details like this, my mind just freezes.

I tried Googling to see if someone has come up with a good process for testing but what I have found are normally a good process of setting up the spreadsheet that makes testing easier. Also, the writers say you have to have good tests but what if I don't set up good tests? What makes a good test?

So I'm struggling with this. I want to set up some kind of automated system that will handle the details and grunt work but I haven't figured out a good way of automating that will generate a good test. But that is my inclination: automate the heck out of it.

I'm just so lazy with the details.