Alpha, tithing would never be done in the first place if the believer didn't have "evidence of the Creator"
testing refers to doctrines regarding the nature of God, the nature of man, or the nature of the relationship between God and man. All heresy distorts one or more of these three fundamental truths that are depicted in scripture.
For instance, the muslims, Jehovah witnesses, mormons, and others, deny Gods nature when they deny Christ. Yet we are told to test that doctrine. Muslims also distort Gods relationship to man, as they believe He is unknowable and beyond us. That is one of the fundamental reasons they so strongly object to Jesus as God, since in their view, God would NEVER condesend to humanity's level...and God would never "have sex".
This is the type of heresy of which I speak...its a complete lack of understanding of the truth and their need for a God that does condescend.
The consistency of their scripture is lacking in this area, fails in "the test".
You have brought up tithing, which is a bahavior of a believer once he has given his life to Christ. Its the working of the Holy Spirit within that allows a cheritable heart.
Muslims may be cheritable, but its a means to an end, they believe its "commanded" and thus necessary for salvation or to be in Gods good standing. We know that charity is not based in or need for salvation, but an offshoot of our love for the Father.