@reggaeguitar

In the fifth good example you can turn left or right when you get to the first cross, how is that not ambiguous?

Yes. What you say is correct when going from LHS 'X' to the RHS 'X'. The line is ambiguous in that direction. But it is not ambigous traversing the line in the other direction (RHS to LHS).

So the line is valid. Because of the rule "Sometimes a line may be valid in one direction but not the other. Such a line is still considered valid."

I still don't understand what exactly you mean by "ambiguous" then. In the fifth good example you can turn left or right when you get to the first cross, how is that not ambiguous?

@reggaeguitar. Does it matter?

If it is false (because ambiguous) or false (because doesn't use every character) then either way it is false, right?

You say the first it false because it's ambiguous because you can go the long way or the short way but the short way does not satisfy the rule "Every line "character" found in the grid must be part of the line. If extras are found then the line is not valid." Am I missing something here? This one should be true based on my understanding

About 10 minutes after posting this, I figured out the reasons why but it was late so I didn't reply. But for future people who are working on this issue and questions about those tests, your answers are invaluable.

First answer:

This one is apparently false for ambiguousness.

I don't think so. This test is one from loopAmbiguous

It is not false for ambiguousness. It is false for being a line - because it is ambiguous.

And it is ambiguous because there is a choice to go short way (1 step) or long way (full loop) to get from either X to the other X

Second answer:

I beieve this one comes under the rule

The corner character (+) must be used for all corners (but only for corners).

If you follow path the left X to the right X you eventually get to the bottom right + and want to go straight ahead. But it is illegal to go straight ahead because + is ONLY for corners!

And if you follow path from bottom-right X to left X you will find yourself at the 3rd + in top row and you wont know whether to go left or right. So it is ambiguous.

So fails in both directions. So false this is not a line.

Two of the paths I don't understand why they should fail:

This one is apparently false for ambiguousness... but I am not clear from the instructions why:

 X-----+  
 X     |  
 |     |  
 |     |  
 +-----+  

The second one is this and all the test says is that it is an edge case but it looks like it has only one legit path (well from each direction). Why is this one false?

  ++++     
 X++++     
     X