What role does the infinitive phrase play in this sentence I am happy to finish my test?

The infinitive phrase "to finish my test" functions as an adverbial phrase in this sentence. It modifies the adjective "happy" by explaining the reason for the speaker's happiness.

Here's a breakdown:

* Infinitive phrase: "to finish my test" (consists of the infinitive "to finish" and its object "my test")

* Adverbial phrase: It answers the question "Why am I happy?"

* Modification: It explains the reason for the speaker's happiness, which is completing the test.

So, the sentence means the speaker is happy *because* they are able to finish their test.