Regarding test 13, you get the error message:
“The sequence “5 * - + 5” = should produce an output of “10” : expected ‘-25’ to equal ‘10’ "
This is referring to user story #13: " If 2 or more operators are entered consecutively, the operation performed should be the last operator entered (excluding the negative ( - ) sign).”
Therefore, for the sequence “5 * - + 5” should end up being computed as “5 + 5” as the the previous operands will be overwritten/ignored.
I haven’t looked through all your code, but it doesn’t appear as if you have any logic to cover this.