Final answer:
Allen's test is used to check the adequacy of collateral circulation to the hand by assessing the patency of the radial and ulnar arteries.
Step-by-step explanation:
The test described in the question is known as Allen's test. It is done to assess the adequacy of the collateral circulation to the hand and evaluate the patency of the radial and ulnar arteries. In this test, the radial artery is compressed while the ulnar artery is still open, and vice versa. By releasing and occluding one artery at a time, it can be determined which artery provides the dominant blood flow to the hand.