OK from what I've learned to date, you actually wouldn't write a test for this, because:
1) it's not good convention to have tests hit the save_spreadsheet method in the first place (since then every test will create a new row of data). Instead you'll want to stub this out.
2) Even if you were ok with that and somehow wanted to write a test, you actually can't write a test in Rspec for a significant number of non-Rails APIs; there's no test feature in this example case that will allow you to look inside the GoogleDrive and see what's there