what is the use of underscore?

In response to @lodimob. Thanks for this kata, Could you add to the description that fillll point that fall on lines are expected to do nothing? I add been confused on the last mixedDrawing tests if my mistake came from this and had to check here.
Also I agree as it as been said already, a bit more small tests cases with mixed drawing would help a lot for debugging. I just can't find what is wrong with my code since every simple test passes.

edit: I think my mistake come from the fact that I expected rectangle to be drawn from top left to down right, and the last test was the only one doing it in reverse manner.

same issue above with more details, closing

Please, someone explain what means this "x" at the beginning

JavaScript
@rscharfer Don't modify the passed argument inp

this O(logN)

its kata can be solved O(N)

Draw the line with 'x' which connects the given points.
If the points are diagonal, a rectangle instead of diagonal line should be drawn

Regarding the points being diagonal, how can we verify this for a rectangle?

For a square, i.e. if the points are diagonal, we can verify with this formula:

|𝑥1−𝑥2|=|𝑦1−𝑦2|

this wouldn't apply for a rectangle

Confirm that the description is OK now.

Added.

In the example has solve("v") = True but not tested in Java Test Cases.