--- test_minus_after_plus()
[0] same lines L2 R2 @L 0 @R 0
[1] minus lines L3 R0 @L 4 @R 10
[2] plus lines L0 R3 @L 4 @R 4
[3] same lines L2 R2 @L 10 @R 10

--- test_plus_after_plus()
[0] same lines L2 R2 @L 0 @R 0
[1] minus lines L3 R0 @L 4 @R 4
[2] plus lines L0 R3 @L 10 @R 4
[3] same lines L2 R2 @L 10 @R 10