Update tests to check for tibbled output

[m-clark]

This has mostly been implemented, but the tests check only for data.frame, and I've been bitten by that at least once.

• [ ] For basic functionality tests, check for tibble rather than data.frame
  • Note that sometimes we actually want a matrix e.g. corr mat, and though this could be tibbled also, I don't really feel the need
• [ ] Note this should get rid of rownames also