xmp2assert

https://github.com/shyouhei/xmp2assert

In ruby we use `# =>` as a comment marker that mean the immediately adjacent expression's expected value. There are gems like xmpfilter / seening_is_believing, which are to generate such comments. They are very useful. But so far we lack feature that does vice-versa; to check if the comment is actually the output of the expression. This is the library that does it.