I understand to attack you need to make attack rolls, but does casting spells require any kind of test before they can be successfully cast or does the player just declare that the spell has been cast assuming they can. The starter rules don't seem to say.
Spells in questions are things like sleep or mage armor.
Best Answer
The rules don't say that any check is required to make a spell work, which is how we know that spells happen automatically: casting requires no rolls to be successful in general.
However, many spells (like Fear) do require rolls against your spell save DC at the other end, to see if particular targeted creatures are affected by the spell as it successfully goes off. Other spells require attack rolls to see if the spell's successful effect hits a creature.