Exodus 16:4

16 ^1-3 On the fifteenth day of the second month after they had left Egypt, the whole company of Israel moved on from Elim to the Wilderness of Sin which is between Elim and Sinai. The whole company of Israel complained against Moses and Aaron there in the wilderness. The Israelites said, “Why didn’t God let us die in comfort in Egypt where we had lamb stew and all the bread we could eat? You’ve brought us out into this wilderness to starve us to death, the whole company of Israel!”

^4-5 God said to Moses, “I’m going to rain bread down from the skies for you. The people will go out and gather each day’s ration. I’m going to test them to see if they’ll live according to my Teaching or not. On the sixth day, when they prepare what they have gathered, it will turn out to be twice as much as their daily ration.”
^6-7 Moses and Aaron told the People of Israel, “This evening you will know that it is God who brought you out of Egypt; and in the morning you will see the Glory of God. Yes, he’s listened to your complaints against him. You haven’t been complaining against us, you know, but against God.”

The verse 16:4 refers to - God providing unfailingly for the Israelites. He promised that He will rain manna down from heaven. Manna is a bread like coriander seed like food from heaven. Basically, God rain down bread(manna) from heaven. God also mentioned the He will test us. The test God is referring to is the test of faith. God promised that He will rain down manna every single day. That means that no one needed to gather more than necessary. It is to test them to see if they have the faith to believe that God will rain down manna tml and that He is a faithful God. He gave specific instructions to the people through Moses regarding the collection and storage of Manna. Everyone was to collect 1 omer of manna per person per day. For weekends, God will allow them to collect twice the amount for the 6th day, because God rests on the 7th day. Those were the tests that God gave Israel. There were still some who failed to obey His commandments. Even though His instructions were clear. If Israelites then can doubt God even though they have a living testimony, how much would we doubt God?