binary: improve tests for invalid numbers

[kytrinyx]

We should have separate tests for:

• alphabetic characters at the beginning of a valid binary number
• alphabetic characters at the end of a valid binary number
• alphabetic characters in the middle of an otherwise valid binary number
• invalid digits (e.g. 2)

If the test suite for binary has test cases that cover these edge cases, this issue can safely be closed.

See exercism/problem-specifications#95

[wobh]

The test suite doesn't cover these cases.

One wrinkle. A submission might use the standard parse-integer which would allow an optional + or - to precede the number and whitespace on either side. Further, parse-integer has a junk-allowed flag so that it will parse the first contiguous numerals it finds in the string (and + or - preceding as before).

http://l1sp.org/cl/parse-integer

[verdammelt]

These new requirements will make it more complicated than simply using parse-integer

[kytrinyx]

@verdammelt is that a bad thing? The original reason I added this was for newbie programmers to actually have to figure out how binary numbers work.

[wobh]

I think it's also good for newbies to understand and use standard tools. I often see (and write) other iterations that implement the exercise more literally. We're also discussing it here: #107

[kytrinyx]

There are other exercises that assume binary and would be good to use the standard tools for (secret handshake, I think, does this. Also maybe allergies, though I think maybe that's just bitwise, so the inputs are decimal but you're expected to think about them in binary).

[kytrinyx]

See exercism/problem-specifications#279

[verdammelt]

@kytrinyx good timing - i was literally (and I do mean literally) about to work on this issue. How did you know?

[kytrinyx]

Hah! That's a delightful coincidence. I've been catching up on email for three days straight, basically, and just accidentally got to this one.

[verdammelt]

Decided to go ahead and push these changes anyway. Not sure how long getting all-your-base exercise out the door will take (ref: exercism/x-common#279.)

[kytrinyx]

Yeah, good call. It could be a while.