The tests are fine, your code fails some tests like the ones with an empty string:

For both encoding and decoding, assume number of rails >= 2 and that passing an empty string will return an empty string.

expected +0 to equal ''

Check your code, not a kata issue.

my encode and decode should work correctly but there is a test cases which got a spaces and i handled them but still there is an errors, you might need to look at it