Edited test_rad_loss_rate unit test to give 100% test coverage of rad_loss_rate().
Edited test_rad_loss_rate unit test to give 100% test coverage of
rad_loss_rate().

dpshelio/sunpy,dpshelio/sunpy,Alex-Ian-Hamilton/sunpy,Alex-Ian-Hamilton/sunpy,dpshelio/sunpy,Alex-Ian-Hamilton/sunpy