Adds and passes the next spec, which takes a two-letter phrase and a shift amount of 1.
Adds and passes specs for taking in a multi-word phrase, first with shift=0 then with shift=1. Passed by adding if-else to loop for passing white space through unchanged.
Adds and passes tests for sending a number into the cipher, first with 0 shift, then 1 shift. Also tested a combo of one number and one letter and shift 1. Passes by adding else if to loop looking for numerical characters (which are stored in an array.)