Final answer:
The sentence in question is an imperative sentence because it gives a command or request politely telling the listener to consider themselves fortunate.
Step-by-step explanation:
The sentence 'Consider yourself fortunate that you missed the test' is an imperative sentence. It's an imperative sentence because it gives a command or a request to someone, even though it is structured in a polite form. The speaker is instructing the listener to regard themselves as lucky or fortunate. Imperative sentences often do not have a clearly stated subject because the subject is usually the person being spoken to, and is understood to be 'you'. Other examples of imperative sentences include commands such as 'Sit down', 'Be quiet', or 'Please pass the salt'.