Added unit test to ensure the label parameter is always constant
Added unit test to ensure the label parameter is always constant

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