I am getting something very similar:
expected:<found the needle at [position ]3>
but was:<found the needle at []3>

Your code is returning a tuple instead of a string.

: ('found the needle at position', 3) should equal 'found the needle at position 3'
: ('found the needle at position', 5) should equal 'found the needle at position 5'
: ('found the needle at position', 30) should equal 'found the needle at position 30'
))