Test identifiers conformity

Make sure the basic identifiers (that is the table name and the equality field name) are valid identifiers in terms of string length and character set.
Different types of identifiers have different restrictions.

It's not because PHPUnit has a `assertEmpty` method, that we cannot do something in the format `assertIsEmpty`. PHPUnit is not holy, and this assertion is quite old. I can point to quite a few ugly things in its API. Also, do you really claim it's unclear to add in the additional word, that makes it actually read well?