Learn English – Single word to use instead of “can’t” or “won’t”

I'm looking for a single word to use instead of can't or won't.

(Single also meaning no hyphenation or conjunctions/contractions. The differences between the words in regard to being unable to vs. being unwilling to can be ignored)

Edit: Some background into this question, when writing Unit Tests in C# I have found it very easy to misread method names that differ solely based on Can vs Cannot. Since many times a unit test will exist with both the pro and contra side. Contractions aren't acceptable for the fact ' is not an allowed character in a method name.