Added unit tests for Chart methods
Added unit tests for Chart methods

vascotenner/holoviews,vascotenner/holoviews,ioam/holoviews,mjabri/holoviews,basnijholt/holoviews,mjabri/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews,basnijholt/holoviews,ioam/holoviews,mjabri/holoviews