What are validation rules and validation test?

A validation rule is simply to make sure that the data is entered correctly into the database (go onto bitesize-ICT-validation and verification for more info)

them yourself, and save yourself getting in trouble on the forums if you need help and possibly getting warned or banned. READ THE RULES. NOT HARD.

A validation rule that is not mandatory.

A validation rule in a database is a rule that prevents the entry of unwanted data. In Microsoft Access for example, a validation rule might prevent someone entering a phone number that is too short...

Yes, they could be either. It depends on what you want to accomplish when you establish a validation rule.