how did penelope plan to find out if she was truly with odyssey

Book XXI Summary:

Penelope retrieves Odysseus' great bow from the storeroom and her maids bear axeheads into the main hall. Penelope explains the game: whoever can string her husband's bow and shoot an arrow through the twelve axeheads will marry her. Telemakhos gives it a try first; he is unable to string the bow three times, then is about to succeed on the fourth when Odysseus gives him a look and he stops. Other suitors fail to string the bow. Meanwhile, Odysseus follows Eumaios and Philoitios outside and reveals his true identity to them, using his scar as proof. After they swear loyalty to him, he instructs them to give him the bow and lock the door when the time comes.

Back in the hall, Eurymakhos fails with the bow, and Anitinoos suggests they postpone the contest, make a sacrifice tomorrow to Apollo, god of archers, and try again. Odysseus asks to try the bow, but Antinoos threatens him not to. Penelope insists the beggar be allowed the opportunity; if he succeeds, she will give him clothing and other gifts. Telemakhos sends her to her room, and then orders Eumaios to give Odysseus the bow. The door and courtyard gate are also locked. Odysseus examines the bow as the suitors mock him. He smoothly strings it as Zeus thunders, then shoots the arrow through the axeheads.