Why don't they just say 'God wipe out the evidences to test our faith ...
Many have used this argument in the past. The problem is that it leads to a conclusion by which the True Believer cannot abide.
First, there is no "pretty good evidence" of an exodus. Indeed there is no evidence at all. This could be a god hiding things, but then writing them up, in such stark detail, in his little book? Not much of a test, I'm sure. More like myth embellished through the eons of telling.
Now for the flood, not only is there no evidence of such a flood there is an abundance of conclusive evidence that such a flood did not occur. So this god would not only have to wipe out all the flood evidence it would also have to purposefully plant all the evidence leading to the conclusion that the flood did not happen.