Expected `mock.plot <- windowedFrequencyShift.plotter(mock_data)` not to throw any errors.
Actually got a <simpleError> with message:
  invalid class "GGbio" object: invalid object for slot "ggplot" in class "GGbio": got class "ggplot2::ggplot", should be or extend class "gg_OR_NULL"

# to do : beef this up with vdiffr : https://github.com/r-lib/vdiffr

Error in `eval(code, test_env)`: object 'mock.plot' not found