Ok, it’s actually simple. Assuming that your macro is in a module,not in one of the sheets, you use:
objExcel.Application.Run "test.xls!dog"
'notice the format of 'workbook name'!macro
For a filename with spaces, encase the filename with quotes.
If you’ve placed the macro under a sheet, say sheet1, just assume sheet1 owns the function, which it does.
objExcel.Application.Run "'test 2.xls'!sheet1.dog"
Notice: You don’t need the macro.testfunction notation you’ve been using.