Necessary promotion to bishop from an actual computer game:

[sje]

Steven, do you have plans to release Symbolic? I guess it would be an interesting program to play and analyse with.

Probably never. If I change my mind on this, I'll let people know.

[AdminX]

Another:
[d]8/4R2P/5pk1/5p2/5P2/7K/7N/6q1 w - - acd 19/43; acn 98710030; acs 24; bm h8=B; ce 3; pv h8=B Qf2 Rg7+ Kh5 Rg3 Qxf4 Bxf6 Qh6 Bd4 f4 Rc3 Kg6+ Kg2;

Okay, it's not clear to me why h8 (B) is the best move here. In fact the 6th move of the PV (Rc3) appears to be a mistake according to Rybka 3. See the position right before Rc3 below.

[d]8/8/7q/4B2k/5p2/6RK/7N/8 w - - 0 6

[sje]

Is there a position which promoting to a rook is required or can I leave the rook out?

Yes. The simplest one arises from the KPK endgame where a promotion to a queen causes stalemate.
[d]8/1P6/k7/8/1K6/8/8/8 w - - 0 1
b8=R TBScore: MateIn7
Ka3 TBScore: Even
Ka4 TBScore: Even
Kb3 TBScore: Even
Kc3 TBScore: Even
Kc4 TBScore: Even
Kc5 TBScore: Even
b8=B TBScore: Even
b8=N+ TBScore: Even
b8=Q TBScore: Even

[Dann Corbit]

[d]kr6/P3npp1/1P6/1Qp1P3/2P2n1p/3p4/4r3/1B1R1K2 w - - acd 19/34+; acn 5642827; acs 2; bm axb8=B; ce 32468; pv axb8=B Rf2+ Kxf2 Kxb8 Qd7 Ned5 Qa7+ Kc8 b7+ Kd7;

[glorfindel]

Is there a position which promoting to a rook is required or can I leave the rook out?

Perhaps the oldest and one of the most beautiful:
Saavedra 1895
[d] 8/8/1KP5/3r4/8/8/8/k7 w - - 0 1

1. c7 Rd6+ 2. Kb5 Rd5+ 3. Kb4 Rd4+ 4. Kb3 Rd3+ 5. Kc2 Rd4 6. c8=R!! {6. c8=Q Rc4+! 7. Qxc4 stalemate} Ra4 7. Kb3 1-0

[sje]

[d]kr6/P3npp1/1P6/1Qp1P3/2P2n1p/3p4/4r3/1B1R1K2 w - - acd 19/34+; acn 5642827; acs 2; bm axb8=B; ce 32468; pv axb8=B Rf2+ Kxf2 Kxb8 Qd7 Ned5 Qa7+ Kc8 b7+ Kd7;

Maybe not:

[PV] 1. axb8=Q+ Kxb8 2. Qd7 Ned5 3. cxd5 Nxd5 4. Qa7+ Kc8 5. Bxd3 Rxe5 6. Ba6+ Kd8 7. Qc7+ Ke8 8. Bb5+ Kf8 9. Qd8+ Re8 10. Qxe8# Score: MateIn10

Even better:

[PV] 1. Rxd3 Nxd3 2. Bxd3 Rc8 3. Bxe2 Kb7 4. Bf3+ Nc6 5. Bxc6+ Rxc6 6. Qa6+ Kxa6 7. a8=Q+ Kxb6 8. Qa7+ Score: MateIn9

[Steelman]

Is there a position which promoting to a rook is required or can I leave the rook out?

Perhaps the oldest and one of the most beautiful:
Saavedra 1895
[d] 8/8/1KP5/3r4/8/8/8/k7 w - - 0 1

1. c7 Rd6+ 2. Kb5 Rd5+ 3. Kb4 Rd4+ 4. Kb3 Rd3+ 5. Kc2 Rd4 6. c8=R!! {6. c8=Q Rc4+! 7. Qxc4 stalemate} Ra4 7. Kb3 1-0

Oh thats right!
This information is not good. Thay means all promotions with any piece need to be looked at. I have to fix that!

But....These positions are mostly if not all endgame positions.
Since I all ready check the queen and knight would it be possible to only add the rook and bishop promotions during the "endgame" only. And of course the pawn which is ready to promote must be on the 6th or 7th rank. So it must be possible to remove some of the under promotions when they are not needed? And still just limit the promotions to queen and knight even in the endgame?

[Dirt]

A few more:
[d]6r1/7P/1R6/5k2/8/4R1K1/8/8 w - - acd 20/20; acn 44329606; acs 20; bm hxg8=B; ce 32764; pv hxg8=B;

A knight looks equally good here.

[Edmund]

Why not just try underpromotions(B/R) in case the queen promotion returns a drawscore. Thats what all these examples have in common.

[Anil]

A few more:
[d]6r1/7P/1R6/5k2/8/4R1K1/8/8 w - - acd 20/20; acn 44329606; acs 20; bm hxg8=B; ce 32764; pv hxg8=B;

A knight looks equally good here.

Analysis/Solution by Chest UCI:

MATE IN 2:
PV= h7g8n f5g5 e3e5
PV= h7g8b f5g5 e3e5
h7g8b f5g5 e3e5
h7g8n f5g5 e3e5