Answer:
Simple sentence
Step-by-step explanation:
The sentence We will do the test later. is a simple sentence.
A simple sentence is a sentence that consists of one independent clause - a clause that can stand alone as a sentence. It contains all elements a sentence should contain - a subject and a predicate, and it expresses a complete thought. The subject here is we, and the predicate is will do. Besides that, this sentence has a clear, complete meaning.
A compound sentence is a sentence that consists of at least two independent clauses.
A complex sentence is a sentence that consists of one independent and at least one dependent clause.