If there was no free will, there would be no point in having us do these "tests" since he already knows the result. Moreover, if a follower decides to defect from his faith because of the gravity of these tests, it would be this god's fault for doing so. Therefore, this god is a sadistic ventriloquist and we are the puppets following his every whim.
The concept of heaven and hell would also be a farce. Since there would be only one outcome (the outcome that this god knows), the people would surely enter their destined realm. The concept of repentance and redemption would be all for naught, another reason to call him a sadistic ventriloquist.
If he already knew that Adam and Eve would eat the fruit and wouldn't want his creation to fall into sin, he would not have created that cursed tree in the first place. But since he supposedly did, then it is either he didn't know the outcome or mankind was meant to sin.
Believers believe that every obstacle in life is a "test" from him. As we all know, we test something in order to know the outcome of certain events. College entrance tests, medical examinations, crash tests, taste tests... All these are needed since we can't see into the future in order to determine whether you're eligible to get into college, whether you need special treatment, whether the car needs better airbags, or whether the soup tastes salty. If this god is omniscient - and by extension, knows all future events, why would he need to test our faith?
On the other hand, if free will did exist, the concept of omniscience would not suffice, since all would be subject to uncertainty. Since he is not omniscient, he wouldn't satisfy the definition that Christians have made.
It's either there is a god and he is a sadistic ventriloquist, or there is no god at all and everything just happens at random.
I'd go for the latter. The thought of a sadistic ventriloquist is just scary...