Here is the whole original list:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 

TEST 1 - two equal parts.
Correct split for this test: 
1 2 3 4 5 6 7 8 9 10 
11 12 13 14 15 16 17 18 19 20 
Now your two parts:
1 2 3 4 5 6 7 8 9 10 
11 12 13 14 15 16 17 18 19 20 
First piece: head at 1; tail at 10
Second piece: head at 11; tail at 20

TEST 2 - first part just first node.
Correct split for this test: 
1 
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
Now your two parts:
1 
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 
First piece: head at 1; tail at 1
Second piece: head at 2; tail at 20

TEST 3 - second part just last node.
Correct split for this test: 
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
20 
Now your two parts:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
20 
First piece: head at 1; tail at 19
Second piece: head at 20; tail at 20