Hmm... I have it a once over when it hit CPAN. Read the POD for the main Excel::Template module. Couldn't get a firm idea of what it's function was. Discarded into my "look at in a few versions time" pile.
So my first suggestion would be a more complete example of what I would be using the darn thing for ;-) It might be there in the other docs - but as a reader I'm just too darn lazy. It needs pointers from the main POD file if they're elsewhere.
I also was at a loss as to how to write the tests. In my rewrite of PDF::Template, I wrote a mockup of pdflib_pl and tested my calls to that module, but there were only some 15 functions used. I'm using more in Spreadsheet::WriteExcel ... can the same method apply?
This may well be me being dim - but can you describe what the difficulty with the tests is? Can you give an example of a piece of behaviour that you're not sure how to test?