The real remedy for a failed Y axis test
In this forum I see a number of posts in which Prusa people recommend fixing the failure of a Y axis test by changing belt tensions. DO NOT DO THIS! It can have very bad consequences including stripping a belt tensioner.
The actual remedy for this issue is located here: https://arachnoid.com/3D_Printing_Prusa_Core_One/index.html#Core_XY_Axis_Alignment
Briefly:
* Tune the belts according to the published instructions, both belts tuned to 85 Hz. This issue is also covered in the above linked article.
* Use the instructions in the above link to carefully, gently correct the relationship between the X and Y axes, so they lie at exactly 90 degrees.
But no matter who says it, DO NOT try to fix this issue by changing belt tensions away from the recommended setting of 85 Hz on both sides.