Final answer:
The infinitive phrase in the sentence acts as an adjective, providing additional information about the subject's emotions.
Explanation:
The infinitive phrase in the sentence 'I am happy to finish my test' plays the role of an adjective. It modifies the subject 'I' and provides more information about the state of being happy.
Learn more about Infinitive phrases and their functions in sentences here:
https://brainly.com/question/30420244
