God's knowledge is constant, complete, and never acquired after ignorance. The Quranic language about Allah "knowing" through tests means that what He eternally knows is brought into open reality, so people are judged with perfect justice.
Why the question feels forceful
The objection is not silly. Some verses say that Allah tests people "until" He knows who is truthful, patient, or striving. A critic argues: if God only knows after the test, then His omniscience is not constant. And if He already knows, why use language that sounds like discovery?
Put strongly, the objection says: either Allah's knowledge changes from not knowing to knowing, or the wording is misleading. That is the real force of the argument.
What the Quran says clearly about God's knowledge
The Quran repeatedly states that Allah's knowledge is total: hidden and open, past and future, actual and possible. These are not isolated lines; they are a major theme of the Quran.
With Him are the keys of the unseen; none knows them except Him. He knows what is on the land and in the sea. Not a leaf falls except that He knows it.
Quran 6:59
No disaster strikes upon the earth or among yourselves except that it is in a register before We bring it into being.
Quran 57:22
The Prophet (PBUH) also taught that Allah's decree is not something He learns as events unfold.
Allah wrote the decrees of the creation fifty thousand years before He created the heavens and the earth.
Sahih Muslim
So any reading of "until We know" that makes Allah ignorant until the test would collide with the Quran's plain teaching and with the established creed of Islam.
What "until We know" means in context
In Arabic, as in English, "know" can mean more than acquiring new information. It can mean to distinguish, expose, verify in the world, or make something known in a way that has consequences. A teacher may say, "I will test the class so I know who studied." That need not mean the teacher had no prior idea; it means the test will reveal it in a just and concrete way.
The Quran itself uses this testing language to show that faith is not a claim left unproven:
Do people think they will be left to say, "We believe," and they will not be tested? We certainly tested those before them, and Allah will surely make evident those who are truthful, and He will surely make evident the liars.
Quran 29:2-3
Classical scholars explained such verses in this sense: Allah already knows eternally, but He tests so that the known reality appears in deeds, and so that reward and punishment are based on what people actually choose and do. Allah does not punish a person merely because He knows what that person would do; He brings the matter into existence with full justice.
What the argument does and does not prove
The argument does prove that the Quran speaks about divine testing in time. Human choices matter. Patience, hypocrisy, courage, and sincerity become visible through real events.
But it does not prove that God's knowledge is limited or intermittent. That conclusion only works if one insists that "know" must always mean "learn after ignorance." The Quran, Arabic usage, and reason do not require that. The stronger reading is that Allah's eternal knowledge never changes, while the world changes and reveals what He already knew.
So the answer is plain: God's omniscience applies constantly. The tests are not for Allah to discover facts; they are for human reality to be manifested, recorded, and judged with perfect justice.