I agree with the others that it's cleanest to do it with two separate checks,

if (/^test\d/ && !/~$/){ ...
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(Note that the + and the .* don't add anything. Anything that matches the above will also match your regexp, and vice versa (except for your broken / in the middle)). There is a way to do it all in one regexp without lookaheads or lookbehinds, though.

if (/^test\d(?:$|.*[^~]$)/){
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Which says that after your first digit, there are either no characters at all, or as many as you like provided the last one isn't a ~.