Remove CalculateAverage from shared_example name/calls
Restructure test suite to hold InputError examples in their own describe-block
Build describe-block for InputError tests; write test expecting appropriate error message for non-integer/-float arguments
Write test expecting a result of 1 with n==1
Write test expecting raising of InputError (with proper message) on n<1
Reword expected InputError message; add additional test for positive-integer factorial calculation
Rework how calc_factorial() verifies input