Update  test/proxy/posts.test.js

1. 
an.Number should be a.Number
an.String should be a.String

And in should.js, all ` as a, an, be, of and have` are dummy getter. They dont have actual meanings, so we can safely ignore them.

2. I think actions like database connection or database mock should be put in `after` or `before` block but not test unit block. 
Test unit should be agnostic about environment.