I guess the test was that if they ate the fruit from that one tree they would die. Sin entered the world and death. Man didn't know what sin was because he didn't know good and evil, just the good. I figure if it was just the good, sin was not there. But I don't think it is a big issue, and we can call it sin if we like.
Ro 5:12 - Wherefore, as by one man
sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
There are a few things I would like to say. First of all, the Bible is the history of man's salvation, and that is the only way to read it. One cannot read it any other way.
Secondly the Tree of Knowledge of Good and Evil was placed there to remind man that although he was created in God's image and likeness, he is not God, but a creation of God. And only God can define what is good and evil. Man cannot define it for himself. As soon as he did that, he decided on his own to legalize abortion, same-sex marriage, etc. .
Man is supposed to trust in God and form a relationship with Him. Man is supposed to look to God for revelation and not obtain knowledge outside of his relationship with God.Through his relationship with God, man will know good and evil. God told man that if he eats from that tree, he will die. Therefore, Adam and Eve were fully aware of the consequences should they disobey God. The sins of Adam and Eve are disobedience and pride.
In the third place, you are correct that Adam's sin entered the world and even into his descendants. Sin and death came to all mankind. And so Cain killed his brother Abel. That was the first human murder. Many other sins took place after that. Murder, abortion, adultry, theft, lying and all manner of sins were committed by man.
In the fourth place, God gave the Ten Commandments because man was so out of control. Even the people He chose to be His chosen ones were so stiff-necked and stubborn. Nevertheless, the Ten Commandments were given to show man who they are.....murderers, adulterers, thieves, liars, and idolaters. The giving of the law says two things: Those who follow the law lead to a good life. Those who violate the law will not lead to a good life, but to death. In other words, wickedness leads to death. That is what the law has been saying. In the New Testament, Jesus simplified the law into two commandments: Love God and love your neighbor. The Ten Commandments are still in these two laws because in order to love one's neighbor, one should not kill them, lie to them, or steal from them.
However, we find that even with the law in place, there are people who still violate the law. The reason being...man has free will. He can either choose to sin or not to sin. God gave free will to man since the very beginning, and this is why we still have murder, stealing, lying, cheating, etc. God has always respected the choices His creatures made even if He doesn't like their choices.
Finally, our loving Father sent His Son to redeem mankind. He came to save sinners. He ate with the cheating tax collectors, the prostitutes, the liars, the thieves, and even with the hypocritical Pharisees because they were the ones who needed Him the most. And out of his 500 disciples, He chose 12 as His closest Apostles. These 12 were the worst of the lot. Later, He even chose Paul, the persecutor of Christians, to be one of His Apostles.
As Christians, we follow in Christ's footsteps so that Christ can be manifested in us. This is the path a Christian choose and this path leads to life while wickedness leads to death and condemnation. The more we follow in His footsteps, the more we conform to Christ. Christ prayed that we would be one with Him just as He is one with the Father. The Bible is the History of man's salvation and should be read in only that way. In other words, one shouldnt even read it as a science textbook.
As a whole, the message of scripture comes down to two things: 1. That God loves us and 2. Repent and live a life of grace. In order for a child to walk, he must first learn to crawl and then stand. The journey to salvation is like that.
God bless.