Added tests for LinearGradient with control points.
Added tests for LinearGradient with control points.

inclement/vispy,QuLogic/vispy,michaelaye/vispy,dchilds7/Deysha-Star-Formation,sh4wn/vispy,RebeccaWPerry/vispy,julienr/vispy,sh4wn/vispy,ghisvail/vispy,RebeccaWPerry/vispy,hronoses/vispy,dchilds7/Deysha-Star-Formation,sbtlaarzc/vispy,ghisvail/vispy,Eric89GXL/vispy,RebeccaWPerry/vispy,sh4wn/vispy,bollu/vispy,kkuunnddaannkk/vispy,srinathv/vispy,drufat/vispy,kkuunnddaannkk/vispy,QuLogic/vispy,srinathv/vispy,drufat/vispy,jay3sh/vispy,julienr/vispy,kkuunnddaannkk/vispy,jay3sh/vispy,michaelaye/vispy,jay3sh/vispy,Eric89GXL/vispy,hronoses/vispy,jdreaver/vispy,sbtlaarzc/vispy,ghisvail/vispy,hronoses/vispy,drufat/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation,srinathv/vispy,michaelaye/vispy,sbtlaarzc/vispy,inclement/vispy,jdreaver/vispy,bollu/vispy,Eric89GXL/vispy,jdreaver/vispy,inclement/vispy,julienr/vispy,QuLogic/vispy