This test case tests the call "extend" from various places.

sdr> /program = Program.PLUS; setFormation(Formation.SQUARED_SET)
|      3Gv  3Bv
| 
| 4B>            2G<
| 
| 4G>            2B<
| 
|      1B^  1G^
sdr> heads lead right
| 4B>  3G<  1B>  2G<
| 
| 4G>  3B<  1G>  2B<
sdr> extend
| 4B>  1B>
| 
| 3G<  2G<
| 
| 4G>  1G>
| 
| 3B<  2B<
sdr> /exit